aoc/alsa: change pcm callbacks to be nonatomic

Pcm callbacks such as triggers are atomic by default. Since the mic
input start cmd sent to AoC takes more than 50 ms, the spin-lock being
used will disable preemption for more than 50ms. So we choose to use
mutex to allow preemption.

As a result, all the pcm callbacks should be nonatomic and
snd_pcm_period_elapsed() should be called within the process
context.

Changes made here are:

- Set pcm->nonatomic as true
- Use mutex instead of spin_lock for aoc_audio_control()
- Use workqueue to update the pcm hw_ptr

Bug: 196817394
Change-Id: Ibc858555b85dedd2560f92cd15e1d059c61f9fce