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