This just adds the defines from the DP 1.2 spec, which we
will use later.

fix some DP MST to 1.2 MST
Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Todd Previte <tprevite@gmail.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>