The hardware supports either size. Also add checks to ensure that only
these two sizes may be used for supplying a LUT.
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Has a nice side-effect that we only update HW for this when it changes now,
rather than every time we do a page flip.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
