Tell the PCI core about host bridge address translation so it can take
care of bus-to-resource conversion for us.
N.B. Leon apparently never uses initial BAR values, so it didn't matter
that we never fixed up the I/O resources from bus address to CPU addresses.
Other sparc uses pci_of_scan_bus(), which sets device resources directly
to CPU addresses, not bus addresses, so it didn't need pcibios_fixup_bus()
either. But by telling the core about the offsets, we can nuke
pcibios_resource_to_bus().