UefiCpuPkg/PiSmmCpuDxeSmm: Remove MTRR field from PSD

https://bugzilla.tianocore.org/show_bug.cgi?id=277

The MTRR field was removed from PROCESS_SMM_DESCRIPTOR
structure in commit:

26ab5ac362

However, the references to the MTRR field in assembly
files were not removed.  Remove the extern reference
to gSmiMtrr and set the Reserved14 field
of PROCESS_SMM_DESCRIPTOR to 0.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>

UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmiException.asm

@@ -23,7 +23,6 @@
 
 EXTERNDEF   SmiPFHandler:PROC
 EXTERNDEF   PageFaultStubFunction:PROC
-EXTERNDEF   gSmiMtrrs:QWORD
 EXTERNDEF   gcSmiIdtr:FWORD
 EXTERNDEF   gcSmiGdtr:FWORD
 EXTERNDEF   gTaskGateDescriptor:QWORD
@@ -245,7 +244,7 @@ gcPsd     LABEL   BYTE
             DD      GDT_SIZE
             DD      0
             DB      24 dup (0)
-            DQ      offset gSmiMtrrs
+            DQ      0
 PSD_SIZE  = $ - offset gcPsd
 
 gcSmiGdtr   LABEL   FWORD