ALSA: lx6464es: Use nonatomic PCM ops

Like the other previous changes, this patch for lx6464es takes the
same strategy for converting to nonatomic PCM ops: replacing spinlock
with mutex, converting the irq tasklet to the threaded irq, and
merging the trigger tasklets back to the trigger callback.

Signed-off-by: Takashi Iwai <tiwai@suse.de>