MdePkg: MmCommunication: Added definition of MM Communication PPI

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3629

MM Communication PPI was defined in PI Specification since v1.5. This
change added definition of such PPI and related GUIDs into MdePkg.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>

Signed-off-by: Kun Qin <kuqin12@gmail.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

MdePkg/MdePkg.dec

@@ -991,6 +991,9 @@
   ## Include/Ppi/MmConfiguration.h
   gEfiPeiMmConfigurationPpi       =  { 0xc109319, 0xc149, 0x450e, { 0xa3, 0xe3, 0xb9, 0xba, 0xdd, 0x9d, 0xc3, 0xa4 } }
 
+  ## Include/Ppi/MmCommunication.h
+  gEfiPeiMmCommunicationPpiGuid   =  { 0xae933e1c, 0xcc47, 0x4e38, { 0x8f, 0xe, 0xe2, 0xf6, 0x1d, 0x26, 0x5, 0xdf } }
+
   #
   # PPIs defined in PI 1.7.
   #