[pulseaudio-discuss] Add support for volume controls from UCM

[arun at accosted.net]

As promised, here's a patch set that allows you to use the
PlaybackVolume and CaptureVolume values in UCM to specify ALSA controls
to use for hardware volume control.

The first two patches are a bit of refactoring that makes things a bit
cleaner while managing extra device port data in the UCM case.

The third patch implements the actual support for volume controls.

Cheers,
Arun