Pull cpu_softintr_p() from trunk.
Ressurect the ad-audiomp branch at request of matt@.

With this commit:

- core audio subsystem made MPSAFE
- eap, btsco drivers made MPSAFE

TODO:

- midi
- convert remaining drivers
- Serialize changes to filters and audio device settings while a read/write
  is in progress.
- Fix other concurrency issues.
- Convert to use kmem_alloc().
- Don't do evil NOWAIT allocations.
- Don't assume sc_intr_lock is a spinlock.
- Add a comment block about the locking.
No need for sc_intr_lock to be a spinlock any more, since we don't have
a hardware interrupt.
Fix a panic and some comments.
Death to NOWAIT.
Convert some more drivers.
Allow hw->mappage to sleep.
Enable subr_pcq.c. The MIDI sequencer will use it to avoid lock order
and context problems.
No need to run the softint at SOFTINT_SERIAL.
Checkpoint work on MIDI.
Checkpoint work in progress.
audiommap() doesn't need a writer lock.
Acquire interrupt level lock for hw->close, on error.
Kill IPL_AUDIO, splaudio().
Checkpoint work in progress.
Make it compile.
- Add a table listing hw_if methods, and which locks are held when called.
- Grab locks in a couple more places.
Missing get_locks() method.
Fix locking for ac97.