they are more like physical addresses in that you can not just
dereference a pointer to access the space. (Also, if you use a
pointer type for such things, gdb will _try_ to deference it.)
- 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.
