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)
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