OvmfPkg: enable stack guard for TDVF

- Set the PcdCpuStackGuard to be true.
- Guard page is set to be not present by Split2MPageTo4K() in
  TdxStartupLib.
- Stack switch is set by InitializeCpuExceptionHandlersEx() in
  CpuExceptionHandlerLib.

Signed-off-by: Jiaqi Gao <jiaqi.gao@intel.com>

OvmfPkg/OvmfPkgX64.dsc

@@ -638,6 +638,7 @@
   #gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable|TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdTdxSetNxForStack|TRUE
+  gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard|TRUE
 
   # Set memory encryption mask
   gUefiOvmfPkgTokenSpaceGuid.PcdTdxPteMemoryEncryptionAddressOrMask|0x0