return a struct device * of attached device, or NULL if device attach failed,
rather than 1/0 for success/failure, so that code that bus code which needs
to know what the child device is doesn't have to open-code a hacked variant
of config_found(). Make config_attach() return struct device *, rather than
void, to facilitate that.
- 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.
argument list. This allows easy 'submatching', which will eliminate a fair
bit of slightly tricky duplicated code from various busses. config_found()
is now a #define in sys/device.h, which invokes config_found_sm().
