UefiCpuPkg/CpuMpPei: Load microcode if found newer revision

Current implementation only loads the latest revision if there is no microcode
loaded. Per IA32 User Manual, we should load the newer revision by comparing
the existing microcode loaded with the updating revision.

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