Merge tag 'tags/virtio_snd-5.12-rc2' into for-next

Merge tag 'tags/virtio_snd-5.12-rc2' into for-next

ALSA: add virtio sound driver

This series implements a driver part of the virtio sound device
specification v8 [1].

The driver supports PCM playback and capture substreams, jack and
channel map controls. A message-based transport is used to write/read
PCM frames to/from a device.

As a device part was used OpenSynergy proprietary implementation.

v7 changes:
 - Moved the snd_pcm_period_elapsed() call from the interrupt handler to the
   kernel worker for being consistent with the non-atomic mode of the PCM
   device.
 - Removed SNDRV_PCM_INFO_RESUME flag. Now ops->prepare() sets the parameters
   for the substream if it was previously suspended.
 - Some additional code readability improvements/comments.

[1] https://lists.oasis-open.org/archives/virtio-dev/202003/msg00185.html

Link: https://lore.kernel.org/r/20210302164709.3142702-1-anton.yakovlev@opensynergy.com