DRAFT [for alsa-lib 1.2.15] USB-Audio: add support for conf.d configurations

alsa-project/alsa-ucm-conf pull request #654 was opened from perexg:

It may be useful to add new or override specific hardware configurations until they are merged to the main USB-Audio.conf file.

BugLink: https://github.com/alsa-project/alsa-ucm-conf/issues/609

Request URL : https://github.com/alsa-project/alsa-ucm-conf/pull/654 Patch URL : https://github.com/alsa-project/alsa-ucm-conf/pull/654.patch Repository URL: https://github.com/alsa-project/alsa-ucm-conf