UefiCpuPkg: Add PCD PcdCpuApLoopMode

UefiCpuPkg: Add PCD PcdCpuApLoopMode

This new PCD is used to specify the AP loop mode during POST phase.

The value 1 means we will place AP in the Hlt-Loop state by HLT instruction.
BSP need to send INIT-SIPI-SIPI to wake up APs.

The value 2 means we will place AP in the deepest C-state by MWAIT instruction.
BSP need to modify the monitor buffer by MONITOR instruction to wake up APs.

The value 3 means we will place AP in the Run-loop state. APs are running.
BSP need to write one semaphore to wake up APs.

Contributed-under: TianoCore Contribution Agreement 1.0
Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Tested-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19341 6f19259b-4bc3-4df7-8a09-765794883524