- general code review and cleanup
- can this be converted to not require PCI_DRIVERS_LEGACY ??
    The irq returned by pcibios_map_irq is a "hwirq" (hardware irq number)
    and pci_assign_irq() assigns this directly to dev->irq, which
    expects a "virq" (virtual irq number).  These numbers are different
    on MIPS.  There is a gross hack to make it work on one
    specific platform, so it can be tested.
- Should this be merged with arch/mips/pci/pci-mt7620.c ??
- ensure device-tree requirements are documented

Cc:  NeilBrown <neil@brown.name>