This updates the valkyriefb driver to the new API.

From Paul Mackerras <paulus@samba.org>:

 "It compiles OK, but I haven't been able to test it.  I have simplified
  the driver quite a bit using the knowledge that there can only ever be
  one valkyrie graphics adaptor in a system - it is the built-in
  graphics adaptor on various ancient mac and powermac machines, and we
  access it at a hard-coded address, so we can only handle one."