UefiCpuPkg: Add STM GUIDs, Protocols, and PCDs

UefiCpuPkg: Add STM GUIDs, Protocols, and PCDs

* Add GUIDed HOB that described MSEG region in SMRAM
* Add SM Monitor Init Protocol
* Add PCD to configure size of SMM exception stack
* Add PCD to configure MSEG region size if it is not
  described by the gMsegSmramGuid GUIDed HOB.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>