UefiCpuPkg/CpuMpPei/X64: Use CodeSegment and DataSegment fields

Using CodeSegment and DataSegment fields in ExchangeInfo instead of the hardcode
MACROs for x64 arch. Switch AP from real mode to long mode directly, so needn't
the CS/DS of protected mode.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Giri Mudusuru <giri.p.mudusuru@intel.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>