Merge remote-tracking branch 'remotes/kraxel/tags/audio-20190924-pull-request' into...

Merge remote-tracking branch 'remotes/kraxel/tags/audio-20190924-pull-request' into staging

audio: documentation fixes.
audio: new backend api (first part of the surround sound patch series).

# gpg: Signature made Tue 24 Sep 2019 07:19:31 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/audio-20190924-pull-request:
  audio: split ctl_* functions into enable_* and volume_*
  audio: common rate control code for timer based outputs
  audio: unify input and output mixeng buffer management
  audio: remove remains of the old backend api
  wavaudio: port to the new audio backend api
  spiceaudio: port to the new audio backend api
  sdlaudio: port to the new audio backend api
  paaudio: port to the new audio backend api
  ossaudio: port to the new audio backend api
  noaudio: port to the new audio backend api
  dsoundaudio: port to the new audio backend api
  coreaudio: port to the new audio backend api
  alsaaudio: port to the new audio backend api
  audio: api for mixeng code free backends
  audio: fix ALSA period-length typo in documentation
  audio: fix buffer-length typo in documentation

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>