UefiCpuPkg/MpInitLib: Add two instances PeiMpInitLib and DxeMpInitLib

UefiCpuPkg/MpInitLib: Add two instances PeiMpInitLib and DxeMpInitLib

Add two MP Initialize Library instances PeiMpInitLib.inf and DxeMpInitLib.inf
with NULL implementation.

One PeiMpInitLib.inf is consumed by PEI MP driver. Another DxeMpInitLib.inf is
consumed by DXE MP driver.

Place MpInitLibStartupAllAPs()/MpInitLibStartupThisAp()/MpInitLibSwitchBSP()/
MpInitLibEnableDisableAP() into PeiMpLib.c and DxeMpLib.c, because they have
the different implementations and will be updated in latter patches.

v5:
  1. Add back PeiExceptionHandlerLib.inf in UefiCpuPkg.dsc. It is removed
     incorrectly.

v4:
  1. Return EFI_UNSUPPORTED instead of EFI_SUCCESS for NULL implementation of
     all Functions.
  2. Sync MpInitLibxxx functions header updating described in v4 part of Patch
     #4.

v3:
  1. Rename MpInitLibSwitchBsp to MpInitLibSwitchBSP to match PI spec

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: Giri P Mudusuru <giri.p.mudusuru@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>