USB-Audio: Add Audient iD14 MkI profile (2708:0002)

USB-Audio: Add Audient iD14 MkI profile (2708:0002)

Expose two logical stereo USB playback pairs, two mono analogue inputs,
and a Direct use case for the raw 4-output/10-input stream.

The device firmware applies monitor-mix attenuation asymmetrically. Initialize
all four gains to unity on every boot or hotplug because the Direct use case
has no verb. Reapply unity when HiFi is selected. Support both the historical
Speaker Playback Volume name and the Monitor Mix Playback Volume name used
by the accepted kernel quirk.

Closes: https://github.com/alsa-project/alsa-ucm-conf/pull/836
Signed-off-by: willyp713 <mrwillporter@gmail.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>