removing PowerMAX_OS support

[Dave Airlie]

This support was added over 7 years ago to XFree86, and a comment went
into Pci.h about 4 years ago saying this is broken.

I'd like to remove this crap from the current tree before 7.0 and just
leave it die... it is mainly hooked into the Pci subsystem and as I''m
fixing it up at the moment I'm surely going to break it further...

I'll code up a patch at some stage if nobody really cares..

Dave.