Change ExitBootServices TPL to CALLBACK, so that a device
can disable BME before IOMMU grants access right.
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
(cherry picked from commit 01df510319)