ArmVirtPkg/PrePi: remove mSystemMemoryEnd

Recording the top of SEC visible system memory in a global variable is
not necessary, and violates the constraints of the SEC/PEI environment,
given that it may execute from NOR flash. So remove it.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>

ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S

@@ -14,8 +14,6 @@
 
 #include <AsmMacroIoLibV8.h>
 
-ASM_GLOBAL ASM_PFX(mSystemMemoryEnd)
-
 ASM_FUNC(_ModuleEntryPoint)
   //
   // We are built as a ET_DYN PIE executable, so we need to process all
@@ -68,8 +66,6 @@ _SetupStackPosition:
   ldr   x2, PcdGet64 (PcdSystemMemorySize)
   sub   x2, x2, #1
   add   x1, x1, x2      // x1 = SystemMemoryTop = PcdSystemMemoryBase + PcdSystemMemorySize
-  adr   x2, mSystemMemoryEnd
-  str   x1, [x2]
 
   // Calculate Top of the Firmware Device
   ldr   x2, PcdGet64 (PcdFdBaseAddress)
@@ -151,5 +147,3 @@ _PrepareArguments:
 
 _NeverReturn:
   b _NeverReturn
-
-ASM_PFX(mSystemMemoryEnd):    .8byte 0

ArmVirtPkg/PrePi/Arm/ModuleEntryPoint.S

@@ -14,8 +14,6 @@
 
 #include <AsmMacroIoLib.h>
 
-ASM_GLOBAL ASM_PFX(mSystemMemoryEnd)
-
 ASM_FUNC(_ModuleEntryPoint)
   //
   // We are built as a ET_DYN PIE executable, so we need to process all
@@ -66,12 +64,10 @@ _SetupStackPosition:
   ADRL  (r12, PcdGet64 (PcdSystemMemorySize))
   ldrd  r2, r3, [r12]
 
-  // calculate the top of memory, and record it in mSystemMemoryEnd
+  // calculate the top of memory
   adds  r2, r2, r1
   sub   r2, r2, #1
   addcs r3, r3, #1
-  adr   r12, mSystemMemoryEnd
-  strd  r2, r3, [r12]
 
   // truncate the memory used by UEFI to 4 GB range
   teq   r3, #0
@@ -159,5 +155,3 @@ _PrepareArguments:
 
 _NeverReturn:
   b _NeverReturn
-
-ASM_PFX(mSystemMemoryEnd):    .quad 0

ArmVirtPkg/PrePi/PrePi.h

@@ -29,8 +29,6 @@
 
 #define SerialPrint(txt)  SerialPortWrite (txt, AsciiStrLen(txt)+1);
 
-extern UINT64 mSystemMemoryEnd;
-
 RETURN_STATUS
 EFIAPI
 TimerConstructor (