Recent changes upstream are breaking fbdev on pmacs.

I haven't had time to go deep into that (but I suspect Linus sees it
too on his own g5 unless he removed offb from his .config).

From what I see, it seems that offb is kicking in by default, reserves
the mmio regions, and then whatever chip driver loads can't access them.

offb is supposed to be a "fallback" driver in case no fbdev is taking
over, it should also be "forced" in with video=ofonly kernel command
line. This logic has been broken.

Ben.