UefiCpuPkg/MtrrLib: Add worker functions not invoke IsMtrrSupported()

UefiCpuPkg/MtrrLib: Add worker functions not invoke IsMtrrSupported()

Abstract some worker functions not to invoke IsMtrrSupported(). They could be
used by other functions to reduce the number of invoking times on
IsMtrrSupported().

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: Michael Kinney <michael.d.kinney@intel.com>
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19153 6f19259b-4bc3-4df7-8a09-765794883524