UefiCpuPkg/MtrrLib: Add notes for usage by BSP/APs
Except for MtrrSetAllMtrrs(), others services are not suggested to be invoked by
APs because they are not necessary and may invoke DEBUG() to dump MTRR setting.
Cc: Feng Tian <feng.tian@intel.com> Cc: Michael Kinney <michael.d.kinney@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: Laszlo Ersek <lersek@redhat.com>