UefiCpuPkg/MpInitLib: Do not wakeup AP if only one processor supported

If MaxLogicalProcessorNumber is only 1, we needn't to wake up APs at all
and needn't to register callback functions.

It could improve boot performance on single supported system.

https://bugzilla.tianocore.org/show_bug.cgi?id=204

Cc: Feng Tian <feng.tian@intel.com>
Cc: Liming Gao <liming.gao@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>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

UefiCpuPkg/Library/MpInitLib/DxeMpLib.c

@@ -290,6 +290,13 @@ InitMpGlobalData (
 
   SaveCpuMpData (CpuMpData);
 
+  if (CpuMpData->CpuCount == 1) {
+    //
+    // If only BSP exists, return
+    //
+    return;
+  }
+
   //
   // Avoid APs access invalid buff data which allocated by BootServices,
   // so we will allocate reserved data for AP loop code.