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

[GitHub pull_request - opened <github@alsa-project.org>]

alsa-project/alsa-ucm-conf pull request #836 was opened from willyp713:

Add UCM2 support for the Audient iD14 MkI USB audio interface (`2708:0002`).

The HiFi use case exposes:

- two logical stereo playback pairs (`Output 1/2` and `Output 3/4`)
- two mono analogue capture devices (`Mic/Line Input 1` and `Mic/Line Input 2`)

The Direct use case preserves the raw 4-output/10-input stream for DAWs. This follows the existing iD14 MkII profile's policy of leaving the state-dependent digital capture channels out of the ordinary desktop profile.

The device's FU12 monitor-mix volume behaves asymmetrically below unity. The card-level `FixedBootSequence` initializes all four channels to 0 dB on boot or hotplug, including when Direct is selected (Direct has no verb). The HiFi enable sequence reapplies unity. A `ControlExists` check supports both the historical `Speaker Playback Volume` control and the `Monitor Mix Playback Volume` name from the accepted kernel quirk:

https://lore.kernel.org/r/20260823015353.686080-1-mrwillporter@gmail.com

Hardware-tested on Bazzite with PipeWire 1.6.8 and kernel `7.2.0-ogc4.1.fc44.x86_64`, including both playback pairs, mono inputs, Direct access, channel isolation, software volume, and a physical USB reconnect. The current upstream validator also passes against:

- alsa-ucm-conf `00175aa645c482111d096c3d8230f182a875d286`
- alsa-tests `53d34b6`

The required `alsa-info.sh` output will be attached to this PR.

Request URL   : https://github.com/alsa-project/alsa-ucm-conf/pull/836
Patch URL     : https://github.com/alsa-project/alsa-ucm-conf/pull/836.patch
Repository URL: https://github.com/alsa-project/alsa-ucm-conf