Merge remote-tracking branch 'origin/master' into staging

* origin/master:
  Allow controlling volume with PulseAudio backend
  configure: pa_simple is not needed anymore
  Do not use pa_simple PulseAudio API
  audio/spice: add support for volume control
  hw/ac97: add support for volume control
  hw/ac97: the volume mask is not only 0x1f
  hw/ac97: remove USE_MIXER code
  audio: don't apply volume effect if backend has VOICE_VOLUME_CAP
  audio: add VOICE_VOLUME ctl