UefiCpuPkg/PiSmmCpuDxeSmm: patch "gSmmCr3" with PatchInstructionX86()

Rename the variable to "gPatchSmmCr3" so that its association with
PatchInstructionX86() is clear from the declaration, change its type to
X86_ASSEMBLY_PATCH_LABEL, and patch it with PatchInstructionX86(). This
lets us remove the binary (DB) encoding of some instructions in
"SmmInit.nasm".

Cc: Eric Dong <eric.dong@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=866
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c

@@ -406,7 +406,7 @@ SmmRelocateBases (
   // Patch ASM code template with current CR0, CR3, and CR4 values
   //
   gSmmCr0 = (UINT32)AsmReadCr0 ();
-  gSmmCr3 = (UINT32)AsmReadCr3 ();
+  PatchInstructionX86 (gPatchSmmCr3, AsmReadCr3 (), 4);
   gSmmCr4 = (UINT32)AsmReadCr4 ();
 
   //