MdePkg/Include: add MmServicesTableLib header file

MdePkg/Include: add MmServicesTableLib header file

SMM has been rebranded as MM, and can be implemented in traditional
mode or standalone mode, using the same prototype for the services
table. Expose this table via MmServicesTableLib, permitting the
respective implementations to expose a traditional or standalone
version.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jagadeesh Ujja <jagadeesh.ujja@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>