PI Enabling: the address of PeiServices Pointer should be

1) Set to preceding of IDT table in PeiCore's entry
2) Migrate to preceding of new memory IDT table when memory is discovery

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@4059 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/PeiServicesTablePointerLib/PeiServicesTablePointer.c

@@ -20,6 +20,12 @@
 
 static EFI_PEI_SERVICES  **gPeiServices;
 
+/**
+  The function set the pointer of PEI services immediately preceding the IDT table
+  according to PI specification.
+  
+  @param    PeiServices   The address of PeiServices pointer.
+**/
 VOID
 EFIAPI
 SetPeiServicesTablePointer (
@@ -70,3 +76,18 @@ PeiServicesTablePointerLibConstructor (
   gPeiServices = PeiServices;
   return EFI_SUCCESS;
 }
+
+/**
+  After memory initialization in PEI phase, the IDT table in temporary memory should 
+  be migrated to memory, and the address of PeiServicesPointer also need to be updated  
+  immediately preceding the new IDT table.
+  
+  @param    PeiServices   The address of PeiServices pointer.
+**/
+VOID
+MigrateIdtTable (
+  IN EFI_PEI_SERVICES  **PeiServices
+  )
+{
+}
+