MdeModulePkg: Add BS+RT+AT variable attribute definition
MdeModulePkg: Add BS+RT+AT variable attribute definition

Add BS+RT+AT variable attribute definition.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chao Zhang <chao.b.zhang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>

git-svn-id: 3158a46dfd52e07d1fda3e32e1ab2e353a00b20f@19785 6f19259b-4bc3-4df7-8a09-765794883524

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2