Add locking to mcd(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. MCDINIT being clear).
- Remove critical_enter/exit when sending a PIO command.
- Use bus_*() instead of bus_space_*().

Tested by:	no one
Add locking to mly(4) and mark MPSAFE.
- Add a per-softc mutex.
- Use mutex as CAM sim lock.
- Use taskqueue_thread instead of taskqueue_swi_giant.
- Use callout(9) instead of timeout(9).
- Use bus_*() instead of bus_space_*().

Tested by:	no one
Cleanups to pst(4):
- Use callout(9) instead of timeout(9).
- Don't bother zero'ing the softc.
- Destroy mutex on detach.

Tested by:	no one