MdePkg: Refine EFI_DARKGRAY definition and comments for EFI_TEXT_ATTR
MdePkg: Refine EFI_DARKGRAY definition and comments for EFI_TEXT_ATTR

It's to follow UEFI spec 2.5.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Eric Jin <eric.jin@intel.com>

git-svn-id: 3158a46dfd52e07d1fda3e32e1ab2e353a00b20f@17366 6f19259b-4bc3-4df7-8a09-765794883524

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