the ->finish method is a relicat from the old day were we never had
hotplugging and allowed the driver to do fixups after all busses
had been scanned.  Nowdays only sd and sr actually implement it,
and both only defer actions to there that should actually happen in
->attach.  Change both drivers to move that code into ->attach,
clenaup the Templates to use C99 initializers and get rid of the
methods.

This also cleans up some very crude race-avoidable code in those
drivers, btw..