Replace selwakeup() with KNOTE() in audio(4)

Replace selwakeup() with KNOTE() in audio(4)

KNOTE() is safe to use at IPL_AUDIO. Remove the now-unnecessary
deferring that uses soft interrupts.

Remove selwakeup() calls from audio_detach() because klist_invalidate()
wakes up any remaining kevent/poll/select waiters.

OK mpi@