devices hanging off controllers, any kind of controller.
A device on isa0 is called at probe(self), then attach(self)
A controller on isa0 is called at probe(self), then all it's children with
defined unit numbers are initialized by calling attach(subdev); next all
subdevices with unit ? are initialized by calling attach(sundev).
Almost all device entry points is now like the vax/sun model (intr being
the weird one)
controllers. New behaviour is that if the standard method fails, try
to recalibrate the drive. Success means the drive exists. patch by
hpeyerl@novatel.cuc.ab.ca (who owns several of these historical
artifacts)
