Trust the settings programmed by the BIOS over what the $PIR says.
Specifically, if the BIOS has programmed an IRQ for a device that doesn't
match the list of valid IRQs for the link, use it anyway as some BIOSes
don't correctly list the valid IRQs in the $PIR. Also, allow the user
to specify an IRQ that $PIR claims is invalid as an override, but emit a
warning in that case.