drm/edid: Add the DMT ID in the comments

To help with matching things to spec, include the DMT ID in the comments
in out DMT mode table.

Cc: "liu,lei" <lei.a.liu@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>