UefiCpuPkg/MpInitLib: Get ApLoopMode and MointorFilter size

Firstly, get ApLoopMode from PcdCpuApLoopMode. If MonitorMwait feature is not
supported, update ApLoopMode to ApHltLoop. If MonitorMwait feature is supported,
get MointorFilter size by CPUID.[EAX=05H]:EBX.BIT0-15.

v5:
  1. Add comment block for enum AP_LOOP_MODE.

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Michael Kinney <michael.d.kinney@intel.com>

UefiCpuPkg/Library/MpInitLib/MpLib.h

@@ -35,6 +35,16 @@
 #include <Library/MtrrLib.h>
 #include <Library/HobLib.h>
 
+//
+// AP loop state when APs are in idle state
+// It's value is the same with PcdCpuApLoopMode
+//
+typedef enum {
+  ApInHltLoop   = 1,
+  ApInMwaitLoop = 2,
+  ApInRunLoop   = 3
+} AP_LOOP_MODE;
+
 //
 // AP reset code information including code address and size,
 // this structure will be shared be C code and assembly code.