Add locking to scd(4) and mark MPSAFE.
- Actually use existing per-softc mutex.
- Use mutex in cdev routines and remove D_NEEDGIANT.
- Use callout(9) instead of timeout(9).
- Don't check for impossible conditions (e.g. SCDINIT being clear).
- Use bus_*() instead of bus_space_*().

Tested by:	no one
Add locking to wds(4) and mark MPSAFE.
- Add per-softc mutex.
- Use mutex for CAM SIM lock.
- Use bus_*() instead of inb() and outb().
- Use bus_alloc_resource_any() when reasonable.

Tested by:	no one