v1:
===
During my PIIX consolidation work [1] I've noticed that both PIIX models have
quite different pci_slot_get_pirq() implementations. These functions seem to
map PCI INTx pins to input pins of a programmable interrupt router which is
AFAIU board-specific. IOW, board-specific assumptions are baked into the device
models which prevent e.g. the whole PIIX4 south bridge to be reusable in the PC
machine.
This series first factors out pci_bus_map_irqs() from pci_bus_irqs() which
then allowes for moving the two board-specific PIIX pci_slot_get_pirq()
funtions into their respective boards. With these changes, the PIIX4 south
bridge could eventually become an alternative to the PIIX3-Frankenstein
solution in the PC machine.