Previously we added a dummy I/O port region even though the R-Car
controller doesn't support PCI port I/O. This resulted in bogus root bus
resources like this:
pci_bus 0000:00: root bus resource [io 0xee080000-0xee0810ff]
pci_bus 0000:00: root bus resource [mem 0xee080000-0xee0810ff]
Drop the unused dummy I/O port region and set struct hw_pci.io_optional so
the ARM PCI code doesn't add a default one for us.