deal with stuff like:
(1) configuring built-in devices,
(2) looking at TC slots configuring any devices found.
The lists of slots, slot locations, etc. and built-in devices
are provided by machine-dependent code. Interrupt handling
is also provided by machine-dependent code, but the MD code provides
hooks so that standard names for 'establish' and 'disestablish'
can be used in drivers.
This code requires <machine/tc_machdep.h>, which defines some
portability types specific to the TurboChannel bus code.
