drm/edid: Rewrite mode parse to use the generic detailed block walk

This brings us in line with the EDID spec recommendation for mode
priority sorting.  We still don't extract all the modes we could from
VTB, but VTB is so rare in the wild that I'm not really concerned.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>