UefiCpuPkg/MpInitLib: Implementation of MpInitLibEnableDisableAP()

v4:
  1. Simply the internal function MpInitLibEnableDisableAP()'s function
     header due to it is duplicated with MpInitLibEnableDisableAP().
v3:
  1. Use CamelCase for mCheckAllAPsEvent, mStopCheckAllApsStatus.

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

@@ -364,6 +364,27 @@ SwitchBSPWorker (
   IN BOOLEAN                   EnableOldBSP
   );
 
+/**
+  Worker function to let the caller enable or disable an AP from this point onward.
+  This service may only be called from the BSP.
+
+  @param[in] ProcessorNumber   The handle number of AP.
+  @param[in] EnableAP          Specifies the new state for the processor for
+                               enabled, FALSE for disabled.
+  @param[in] HealthFlag        If not NULL, a pointer to a value that specifies
+                               the new health status of the AP.
+
+  @retval EFI_SUCCESS          The specified AP was enabled or disabled successfully.
+  @retval others               Failed to Enable/Disable AP.
+
+**/
+EFI_STATUS
+EnableDisableApWorker (
+  IN  UINTN                     ProcessorNumber,
+  IN  BOOLEAN                   EnableAP,
+  IN  UINT32                    *HealthFlag OPTIONAL
+  );
+
 /**
   Get pointer to CPU MP Data structure from GUIDed HOB.