Complete support for "Pro" USB multichannel cards

[perexg]

• channel split using alsa-lib
• channel split inside app
• channel split hide the specific configs (alsa-lib, app side support)
• mixer control remap using alsa-lib
• simplify the mixer control remap

[perexg]

Guide from Peter Wedder: https://gist.github.com/brndd/ccec98a575f7c0422d50402937439227

Related commits:

• 9d16a3b Add profile for Behringer UMC204HD
• 701775d Behringer UMC204HD - change the default mixer profile
• f4330c2 Add direct hardware profile for UMC204HD

Related alsa-lib commits:

• alsa-project/alsa-lib@46e991c use-case.h: add SND_USE_CASE_DEV_DIRECT define
• alsa-project/alsa-lib@d7d5c72 ucm: implement MacroDefine and Macro subtree evaluation
• alsa-project/alsa-lib@11ec9e4 ucm: allow passing variables through ucm open string
• many related fixes in the current https://github.com/alsa-project/alsa-lib repo (last commit alsa-project/alsa-lib@55340cf)

[perexg]

All issues should be resolved now.

Test configs (requires very latest alsa-lib): master...perexg:macro-split

@brndd : Could you look to https://github.com/alsa-project/alsa-ucm-conf/blob/1efadcdd15802c9c6aa39c04fe52afd689aac00d/ucm2/USB-Audio/Behringer/UMC204HD-HiFi.conf , if the configuration looks more easy in your eyes now? It would be also nice, if you can test the latest changes, but the alsa-lib library must be upgraded to latest (unreleased) code.

[brndd]

It does look simpler, yes, and most importantly more copy-pasteable.

I will test it, but it will take me until next week to find the time to do so. I haven't compiled and set up alsa-lib before, so it'll probably take me some time to figure it out.

[perexg]

Merged branch with multiple changes for the recent alsa-lib: master...perexg:macro / https://github.com/perexg/alsa-ucm-conf/tree/macro .

[perexg]

I've applied all my changes to the main repository. Open separate issue / pull requests to resolve possible regressions.

[brndd]

Looks like the changes landed in Fedora stable before I got around to testing them -- but now that they're in stable, I can verify that they indeed do work ;-)

Thanks!