breakage:
- call PCIB_ROUTE_INTERRUPT() regardless of how valid the intline looks.
Some alphas leave garbage in the intline and leave the intr mapping
to OS platform support routines that map slots/buses to intlines
- Down in the alpha pci code, first try platform.pci_intr_route() and
if it doesn't exist or returns garbage, just read the intline out of
config space.
tested on AS500 (garbage in intline) and UP1000 (PC-like, intline is valid)
Note that a nice little hack like the APIC_IO section of pci_cfgregread()
is not workable. This is because the calling interface for
alpha_pci_route_interrupt() requires us to figure out the bus/slot/etc
from a device_t. At pci_read_device() time, we don't have a device_t
for the bus/slot/func in question.