UefiCpuPkg/SmmCpuFeaturesLibStm: Add STM library instance

Add a new instances of the SmmCpuFeaturesLib that is used by
platforms to enable the SMI Transfer Monitor(STM) feature.
This new instance is in the same directory as the default
SmmCpuFeaturesLib instance in order to share source files.

The DSC file is updated to build both SmmCpuFeatureLib
instances and to build two versions of the PiSmmCpuDxeSmm
module using each of the SmmCpuFeatureLib instances.

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>