This improves the config space access routines on G5, by adding a
generic helper function to locate the pci_controller structure (to be
used by an upcoming new platform too) and cleaning up the pmac routines.

It includes the fix to skip devices that aren't present in the OF tree
that is necessary for newer G5 desktop models.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>