ArmPlatformPkg/Documentation: remove outdated porting manual

Having a special porting manual for ARM platforms in general suggests
that ARM platforms are fundamentally different from ones based on other
architectures that are supported by UEFI. There may be some truth to
that, but the porting manual in Documentation/ArmPlatformPkg.txt is
hopelessly outdated, and did not give the best advice in the first
place*. So remove it.

* ArmPlatformLib as the mother of all platform abstractions is rather
  unwieldy, and using ArmVExpressLibCTA9x4 as a template is not that
  great an idea either.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

ArmPlatformPkg/Documentation/ArmPlatformPkg.txt

@@ -1,74 +0,0 @@
-Porting UEFI to a ARM platform :
---------------------------------
-1. Create the new platform directory under ArmPlatformPkg
-
-2. Create its DSC and FDF files into this new directory. These files can be copied from ArmVExpress-CTA9x4.dsc and ArmVExpress-CTA9x4.fdf; and adapted following the requirement of your platform. 
-
-3. Set up the PCDs required by ArmPlatformPkg in your FDF or DSC files 
-
-4. Implement 'ArmPlatformLib' for your platform following the interface defined by ArmPlatformPkg\Include\Library\ArmPlatformLib.h.
-
-
-PCDs	Description :
--------------------
-
-# Firmware Device / Volume
-gArmTokenSpaceGuid.PcdSecureFdBaseAddress       : Base address of your Secure Firmware Device 
-gArmTokenSpaceGuid.PcdSecureFdSize              : Size in byte of your Secure Firmware Device.
-gArmTokenSpaceGuid.PcdFdBaseAddress       : Base Address of your Non-Secure/Normal World Firmware Device.
-gArmTokenSpaceGuid.PcdFdSize              : Size in bytes of your Non-Secure/Normal World Firmware Device 
-
-# Stacks
-gArmPlatformTokenSpaceGuid.PcdCPUCoresSecStackBase             : Base of Secure Stack for Secure World
-gArmPlatformTokenSpaceGuid.PcdCPUCoreSecPrimaryStackSize       : Size of the stack for the Primary Core in Secure World
-gArmPlatformTokenSpaceGuid.PcdCPUCoreSecSecondaryStackSize     : Size of the stack for the Secondary Cores in Secure World
-gArmPlatformTokenSpaceGuid.PcdCPUCoresSecMonStackBase          : Base of Stack for Monitor World
-gArmPlatformTokenSpaceGuid.PcdCPUCoreSecMonStackSize           : Size of the stack for each cores
-gArmPlatformTokenSpaceGuid.PcdCPUCoresStackBase                : Base of SEC Stack for Normal World
-gArmPlatformTokenSpaceGuid.PcdCPUCorePrimaryStackSize          : Size of the stack for the Primary Core
-gArmPlatformTokenSpaceGuid.PcdCPUCoreSecondaryStackSize        : Size of the stack for the Secondary Core
-
-# CPU / Architectural controllers
-gArmTokenSpaceGuid.PcdGicDistributorBase        : Base address of the Distributor of your General Interrupt Controller
-gArmTokenSpaceGuid.PcdGicInterruptInterfaceBase : Base address of the Interface of your General Interrupt Controller
-
-# Memory Regions
-gArmPlatformTokenSpaceGuid.PcdSystemMemoryUefiRegionSize  : Size of the region reserve for PI & UEFI
-gArmTokenSpaceGuid.PcdSystemMemoryBase                    : Base Address of the System Memory (DRAM)
-gArmTokenSpaceGuid.PcdSystemMemorySize                    : Size of the System Memory (DRAM)
-
-# Features
-gArmPlatformTokenSpaceGuid.PcdSystemMemoryInitializeInSec : TRUE if System Memory initialized by the SEC phase
-gArmPlatformTokenSpaceGuid.PcdSendSgiToBringUpSecondaryCores : TRUE if the PrePi or PrePeiCore modules have to send an SGI to resume the excution of the secondary cores 
-
-# Boot Manager
-gArmPlatformTokenSpaceGuid.PcdDefaultBootDescription      : Description of the Default Boot Entry
-gArmPlatformTokenSpaceGuid.PcdDefaultBootDevicePath       : DevicePath of the Default Boot Entry
-gArmPlatformTokenSpaceGuid.PcdDefaultBootArgument         : Argument for the Default Boot Entry
-gArmPlatformTokenSpaceGuid.PcdDefaultBootType             : Define the binary type of the Default Boot Entry (0=EFI application, 1=Linux kernel with ATAG support, 2=Linux Kernel with FDT support)  
-gArmPlatformTokenSpaceGuid.PcdPlatformBootTimeOut         : Timeout before booting on the Device Boot entry (by default the auto boot is skipped)
-gArmPlatformTokenSpaceGuid.PcdDefaultConInPaths           : List of Device Path use for the Console Input
-gArmPlatformTokenSpaceGuid.PcdDefaultConOutPaths          : List of Device Path use for the Console Output
-
-
-FAQ :
------
-# When to use PrePi or PrePeiCore ?
-- PrePi: when the memory has already been initialized by the first stage boot loader
-    Boot sequence: PlatformFirmware/PrePi/Dxe/Bds
-    Example: Beagle Board
-
-- PrePeiCore: when the firmware is started from XIP memory and in Secure world. The PeiCore shadows the firmware itself in System Memory (DRAM)
-    Boot sequence: Sec/PrePiCore/PeiCore/Dxe/Bds
-    Example: ARM Versatile Express
-
-See:
-- ArmPlatformPkg/Documentation/ARM-EDK2-Overview.png
-- ArmPlatformPkg/Documentation/ArmPlatformLib-Full-Boot.png
-- ArmPlatformPkg/Documentation/ArmPlatformLib-2nd-Stage.png
-
-# What is the PcdStandalone
-gArmPlatformTokenSpaceGuid.PcdStandalone=FALSE is used on ARM Development Platforms during the development stage.
-To avoid to reflash the NOR Flash after each build, the SEC (in NOR Flash) intializes thd DRAM and wait until the Normal World firmware is copied into the DRAM.
-Copying the firmware in DRAM is much faster than reflashing the NOR Flash. It is also more convenient to debug the firmware form DRAM than NOR Flash (eg: use of software breakpoint)
-