UefiCpuPkg/PiSmmCpu: Check GCD and UEFI mem attrib table.

1) UefiCpuPkg/PiSmmCpu: Check for untested memory in GCD

It treats GCD untested memory as invalid SMM
communication buffer.

2) UefiCpuPkg/PiSmmCpu: Check EFI_RUNTIME_RO in UEFI mem attrib table.

It treats the UEFI runtime page with EFI_MEMORY_RO attribute as
invalid SMM communication buffer.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>

UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c

@@ -16,6 +16,8 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
 #include "PiSmmCpuDxeSmm.h"
 
+UINT8                               mPhysicalAddressBits = 32;
+
 /**
   Create PageTable for SMM use.