Lock the scsi_low code and the drivers which use it along with other
related cleanups:
- Require each driver to initalize a mutex in the scsi_low_softc that
  is shared with the scsi_low code.  This mutex is used for CAM SIMs,
  timers, and interrupt handlers.
- Replace the osdep function switch with direct calls to the relevant
  CAM functions and direct manipulation of timers via callout(9).
- Collapse the CAM-specific scsi_low_osdep_interface substructure
  directly into scsi_low_softc.
- Use bus_*() instead of bus_space_*().
- Return BUS_PROBE_DEFAULT from probe routines instead of 0.
- No need to zero softcs.
- Pass 0ul and ~0ul instead of 0 and ~0 to bus_alloc_resource().
- Spell "dettach" as "detach".
- Remove unused 'dvname' variables.
- De-spl().

Tested by:	no one