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/MpEqu.inc

@@ -92,6 +92,7 @@ struc MP_CPU_EXCHANGE_INFO
   .ModeHighSegment:              CTYPE_UINT16 1
   .Enable5LevelPaging:           CTYPE_BOOLEAN 1
   .SevEsIsEnabled:               CTYPE_BOOLEAN 1
+  .SevSnpIsEnabled               CTYPE_BOOLEAN 1
   .GhcbBase:                     CTYPE_UINTN 1
 endstruc