MdePkg/BaseLib: Add a new VMGEXIT instruction invocation for SVSM

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654

The SVSM specification relies on a specific register calling convention to
hold the parameters that are associated with the SVSM request. The SVSM is
invoked by requesting the hypervisor to run the VMPL0 VMSA of the guest
using the GHCB MSR Protocol or a GHCB NAE event.

Create a new version of the VMGEXIT instruction that will adhere to this
calling convention and load the SVSM function arguments into the proper
register before invoking the VMGEXIT instruction. On return, perform the
atomic exchange on the SVSM call pending value as specified in the SVSM
specification.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

MdePkg/Library/BaseLib/BaseLib.inf

@@ -187,6 +187,7 @@
   Ia32/XGetBv.nasm
   Ia32/XSetBv.nasm
   Ia32/VmgExit.nasm
+  Ia32/VmgExitSvsm.nasm
 
   Ia32/DivS64x64Remainder.c
   Ia32/InternalSwitchStack.c | MSFT
@@ -328,6 +329,7 @@
   X64/XGetBv.nasm
   X64/XSetBv.nasm
   X64/VmgExit.nasm
+  X64/VmgExitSvsm.nasm
   ChkStkGcc.c  | GCC
 
 [Sources.EBC]