MdePkg: Move duplicate EFI_AP_PROCEDURE typedef to a common location

EFI_AP_PROCEDURE was defined equivalently in two locations:
1. MdePkg/Include/Pi/PiSmmCis.h
2. MdePkg/Include/Protocol/MpService.h

This change moves the definition to a common file:
* MdePkg/Include/Pi/PiDxeCis.h

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9470 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Include/Pi/PiDxeCis.h

@@ -695,4 +695,19 @@ typedef struct {
 
 typedef DXE_SERVICES EFI_DXE_SERVICES;
 
+
+/**
+  Function prototype for invoking a function on an Application Processor.
+
+  This definition is used by the UEFI MP Serices Protocol, and the
+  PI SMM System Table.
+
+  @param[in,out] Buffer  Pointer to private data buffer.
+**/
+typedef
+VOID
+(EFIAPI *EFI_AP_PROCEDURE)(
+  IN OUT VOID  *Buffer
+  );
+
 #endif