PPC: Uninorth config space accessor

The Uninorth PCI bridge requires different layouts in its PCI config space
accessors.

This patch introduces a conversion function that makes it compatible with
the way Linux accesses it.

I also kept an OpenBIOS compatibility hack in. I think it'd be better to
take small steps here and do the config space access rework in OpenBIOS
later on. When that's done we can remove that hack.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
