BIT0: This is to control if a platform wants to enable VTd based protection during boot. BIT1: This is to control if a platform wants to keep VTd enabled at ExitBootService. The default configuration is BIT0:1, BIT1:0. Cc: Star Zeng <star.zeng@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Jiewen Yao <jiewen.yao@intel.com> Reviewed-by: Star Zeng <star.zeng@intel.com>