MdePkg: Add the header file for UEFI PI Multi-processor PPI

The MP Services PPI is installed by some platform or chipset-specific PEIM
that abstracts handling multiprocessor support.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17234 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/MdePkg.dec

@@ -780,6 +780,9 @@
 
   ## Include/Ppi/Graphics.h
   gEfiPeiGraphicsPpiGuid             = { 0x6ecd1463, 0x4a4a, 0x461b, { 0xaf, 0x5f, 0x5a, 0x33, 0xe3, 0xb2, 0x16, 0x2b } }
+  
+  ## Include/Ppi/MpServices.h
+  gEfiPeiMpServicesPpiGuid           = { 0xee16160a, 0xe8be, 0x47a6, { 0x82, 0xa, 0xc6, 0x90, 0xd, 0xb0, 0x25, 0xa } }