OvmfPkg/CcExitLib: Update TDVMCALL_EXPOSE_REGS_MASK

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4696

Refer to the [GHCI] spec, TDVF should clear the BIT5 for RBP in the mask.

Reference:
[GHCI]: TDX Guest-Host-Communication Interface v1.5
https://cdrdv2.intel.com/v1/dl/getContent/726792

Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Ceping Sun <cepingx.sun@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Min Xu <min.m.xu@intel.com>

OvmfPkg/Library/CcExitLib/X64/TdVmcallCpuid.nasm

@@ -9,7 +9,7 @@
 DEFAULT REL
 SECTION .text
 
-%define TDVMCALL_EXPOSE_REGS_MASK       0xffec
+%define TDVMCALL_EXPOSE_REGS_MASK       0xffcc
 %define TDVMCALL                        0x0
 %define EXIT_REASON_CPUID               0xa