MdePkg/Include/Ppi: Add back gEdkiiPeiMpServices2PpiGuid

Commit aef50446ce
removed gEdkiiPeiMpServices2PpiGuid from UefiCpuPkg.dec
which causes build breaks if an INF [Ppis] section
lists gEdkiiPeiMpServices2PpiGuid. There is no method
for a DEC file for conditionally declare a PPI.

In order to support the migration from use of
gEdkiiPeiMpServices2PpiGuid to the preferred use of the
gPeiMpServices2Ppi, update MpServices2.h in MdePkg
to define EDKII_PEI_MP_SERVICES2_PPI_GUID and
EDKII_PEI_MP_SERVICES2_PPI.

All references to the EDK II PEI MP Services 2 PPI can be
removed after all downstream consumers have had a chance
to perform the migration.

Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>

MdePkg/Include/Ppi/MpServices2.h

@@ -280,15 +280,13 @@ struct _EFI_PEI_MP_SERVICES2_PPI {
 
 extern EFI_GUID  gEfiPeiMpServices2PpiGuid;
 
-// For backwards compatability. To be removed.
-#ifdef ENABLE_DEPRECATED_EDKII_MP_SERVICES2
-
+//
+// The EDK II PEI MP Services 2 PPI has been replaced by the PEI MP Services 2
+// PPI in the MdePkg. The following definitions are only present for backwards
+// compatibility and will be removed in the future.
+//
 #define EDKII_PEI_MP_SERVICES2_PPI_GUID  EFI_PEI_MP_SERVICES2_PPI_GUID
 
 typedef EFI_PEI_MP_SERVICES2_PPI EDKII_PEI_MP_SERVICES2_PPI;
 
-#define gEdkiiPeiMpServices2PpiGuid  gEfiPeiMpServices2PpiGuid
-
-#endif
-
 #endif

MdePkg/MdePkg.ci.yaml

@@ -165,6 +165,7 @@
             "gEfiPeiMmAccessPpiGuid=gPeiSmmAccessPpiGuid",
             "gPeiSmmControlPpiGuid=gEfiPeiMmControlPpiGuid",
             "gEfiPeiMmCommunicationPpiGuid=gEfiPeiSmmCommunicationPpiGuid",
+            "gEdkiiPeiMpServices2PpiGuid=gEfiPeiMpServices2PpiGuid",
             ]
     },