MdePkg: Fix PI Multi-processor PPI header file include issue

MdePkg: Fix PI Multi-processor PPI header file include issue

Multi-processor PPI header file 'Ppi/Mpservices.h' uses a function
prototype EFI_AP_PROCEDURE which is defined in 'Pi/PiDxeCis.h' (DXE header
file).

This will cause a build fail when 'Ppi/Mpservices.h' is included in a PEI
module.

Since both phase support multi-processor service now, function prototype
EFI_AP_PROCEDURE should be moved to 'Pi/PiMultiPhase.h'. The move is a
compatible change and will not affect other codes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17450 6f19259b-4bc3-4df7-8a09-765794883524