UefiCpuPkg/MpInitLib: Implementation of MpInitLibSwitchBSP()

UefiCpuPkg/MpInitLib: Implementation of MpInitLibSwitchBSP()

v4:
  1. Simply the internal function SwitchBSPWorker()'s comment header
     due to it is duplicated with MpInitLibSwitchBSP().

v3:
  1. Rename MpInitLibSwitchBsp to MpInitLibSwitchBSP.

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>