back on timer 1 interrupts if none is specified.
Only set up timer 1 is the driver is using timer 1 interrupts.
Don't claim the interrupt but allow them to be passed on to other
handlers.
- split softc size and match/attach out from cfdriver into
a new struct cfattach.
- new "attach" directive for files.*. May specify the name of
the cfattach structure, so that devices may be easily attached
to parents with different autoconfiguration semantics.
mark