drm: make mode numbers no change by comparing probed modes

The mode list sets all the output modes to UNVERIFIED, then probes a new list,
If a mode is on the new list and not on the old, it adds it to the old,
if a mode is on the new list and old, it just updates the status to the new
mode status.
If a mode is on the old list and not on the new, prune invalid modes should
remove all UNVERIFIED modes