UefiCpuPkg/MpLib: add support to register GHCB GPA when SEV-SNP is enabled

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

An SEV-SNP guest requires that the physical address of the GHCB must
be registered with the hypervisor before using it. See the GHCB
specification section 2.3.2 for more details.

Cc: Michael Roth <michael.roth@amd.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Ray Ni <ray.ni@Intel.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

UefiCpuPkg/Library/MpInitLib/MpLib.h

@@ -222,6 +222,7 @@ typedef struct {
   //
   BOOLEAN            Enable5LevelPaging;
   BOOLEAN            SevEsIsEnabled;
+  BOOLEAN            SevSnpIsEnabled;
   UINTN              GhcbBase;
 } MP_CPU_EXCHANGE_INFO;
 
@@ -291,6 +292,7 @@ struct _CPU_MP_DATA {
   BOOLEAN        WakeUpByInitSipiSipi;
 
   BOOLEAN        SevEsIsEnabled;
+  BOOLEAN        SevSnpIsEnabled;
   UINTN          SevEsAPBuffer;
   UINTN          SevEsAPResetStackStart;
   CPU_MP_DATA    *NewCpuMpData;