The layer registration allows to handle an extra functionality
on top of the control API. It can be used for the audio
LED control for example.
Signed-off-by: NJaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20210317172945.842280-3-perex@perex.czSigned-off-by: NTakashi Iwai <tiwai@suse.de>