UefiCpuPkg/SmmCpuFeaturesLib: Split into two files

UefiCpuPkg/SmmCpuFeaturesLib: Split into two files

Split the default implementation of the SmmCpuFeaturesLib
into two files to prepare for the addition of the STM
specific SmmCpuFeaturesLib implementation.  The STM
specific implementation installs a different SMI entry
handler and initialize the MSEG specific MSR at the end
of SmmCpuFeaturesInitializeProcessor().

This patch does not introduce any functional changes
to the default implementation of the SmmCpuFeaturesLib.

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>