Add a new PCM control operation to update the stream volume on the
audio backend.  The argument given is a SWVoiceOut/SWVoiceIn.

v4:
- verified other backends didn't fail/assert on this new control
  they randomly return 0 or -1, but we ignore return value.

Signed-off-by: Marc-Andr? Lureau <marcandre.lureau@redhat.com>
Signed-off-by: malc <av1474@comtv.ru>