OvmfPkg/ResetVector: Save the encryption mask at boot time

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108

The early assembler code performs validation for some of the SEV-related
information, specifically the encryption bit position. To avoid having to
re-validate the encryption bit position as the system proceeds through its
boot phases, save the validated encryption bit position in the SEV-ES work
area for use by later phases.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <2609724859cf21f0c6d45bc323e94465dca4e621.1610045305.git.thomas.lendacky@amd.com>

OvmfPkg/Include/Library/MemEncryptSevLib.h

@@ -29,6 +29,8 @@ typedef struct _SEC_SEV_ES_WORK_AREA {
   UINT8    Reserved1[7];
 
   UINT64   RandomData;
+
+  UINT64   EncryptionMask;
 } SEC_SEV_ES_WORK_AREA;
 
 /**