UefiCpuPkg/MpInitLib: Allocate and initialize memory of MP Data buffer

UefiCpuPkg/MpInitLib: Allocate and initialize memory of MP Data buffer

v5:
  1. Add comment block for enum AP_INIT_STATE and structure CPU_AP_DATA.
  2. Add more comment for structure CPU_INFO_IN_HOB.
  3. Add more clarification in structure _CPU_MP_DATA for those fields
     pass from PEI to DXE.

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>