firewire: fw-ohci: PPC PMac platform code

Copied from ohci1394.c.  This code is necessary to prevent machine check
exceptions when reloading or resuming the driver.

Tested on a 1st generation PowerBook G4 Titanium, which also needs the
pci_probe() hunk.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

I was able to reproduce the system exception on resume with a 3rd-gen
Titanium PowerBook G4 667, and this patch does let the system resume
successfully now.

Not quite clear if there was possibly an updated version coming using
pci_enable_device() instead of the pair of pmac_call_feature() calls,
but either way, this is a definite must-have, at least for older ppc
macs -- my Aluminum PowerBook G4/1.67 suspends and resumes without this
patch just fine.

Signed-off-by: Jarod Wilson <jwilson@redhat.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>