UefiCpuPkg/MpInitLib: Implementation of MpInitLibEnableDisableAP()

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>