indirect bus code framework) from Jason Thorpe. This allows us to dump
bus_scan() and bus_print(), and move bus_peek() and bus_mapin() to the
NuBus code (since they'll eventually go away, anyway).
second argument. The NuBus autoconfig code had to be reorganized as a
result of this, and looks much more like a directly-attached bus now.
These changes eliminate __BROKEN_INDIRECT_CONFIG.
Also change the device probing scheme to use something a bit more rational.
A current side-effect is that nubus cards are double-mapped. I expect
to fix that shortly.
Also change splclock() to block everything but serial hardware interrupts.
