ArmVirtualizationPkg: allow patchable PCD for device tree base address

To allow a runtime self relocating PrePi instance to discover the base
address of the device tree at runtime, allow the use of a patchable PCD
for gArmVirtualizationTokenSpaceGuid.PcdDeviceTreeInitialBaseAddress.
We will not be using the build time patch tool in this case, but using
a patchable PCD will make the build system aware that its value is not
a compile time constant.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16957 6f19259b-4bc3-4df7-8a09-765794883524

ArmPlatformPkg/ArmVirtualizationPkg/ArmVirtualizationPkg.dec

@@ -34,7 +34,7 @@
   gArmVirtualizationTokenSpaceGuid = { 0x0B6F5CA7, 0x4F53, 0x445A, { 0xB7, 0x6E, 0x2E, 0x36, 0x5B, 0x80, 0x63, 0x66 } }
   gEarlyPL011BaseAddressGuid       = { 0xB199DEA9, 0xFD5C, 0x4A84, { 0x80, 0x82, 0x2F, 0x41, 0x70, 0x78, 0x03, 0x05 } }
 
-[PcdsFixedAtBuild]
+[PcdsFixedAtBuild, PcdsPatchableInModule]
   #
   # This is the physical address where the device tree is expected to be stored
   # upon first entry into UEFI. This needs to be a FixedAtBuild PCD, so that we

ArmPlatformPkg/ArmVirtualizationPkg/Library/ArmVirtualizationPlatformLib/Virt.c

@@ -96,7 +96,7 @@ ArmPlatformInitializeSystemMemory (
   ASSERT (HobData != NULL);
   *HobData = 0;
 
-  DeviceTreeBase = (VOID *)(UINTN)FixedPcdGet64 (PcdDeviceTreeInitialBaseAddress);
+  DeviceTreeBase = (VOID *)(UINTN)PcdGet64 (PcdDeviceTreeInitialBaseAddress);
   ASSERT (DeviceTreeBase != NULL);
 
   //