ALSA: usb-audio: scarlett2: Add support for "input-other" notify

Some models allow the level and pad settings to be controlled from the
front-panel of the device. For these, the device will send an
"input-other" notification to prompt the driver to re-read the status
of those settings.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/06289a7697455e96b7dbdfd2d384d4b20f8df6e0.1624379707.git.g@b4.vu


Signed-off-by: Takashi Iwai <tiwai@suse.de>