ALSA: scarlett2: Add Gen 4 firmware 2417 front-panel controls

ALSA: scarlett2: Add Gen 4 firmware 2417 front-panel controls

Firmware 2417 for the Scarlett 4th Gen Solo, 2i2, and 4i4 added two
new front-panel features: a LED brightness setting (High/Medium/Low)
and an idle sleep timeout. Add ALSA controls to expose them:

- "Front Panel Brightness": enum (High/Medium/Low)
- "Front Panel Sleep Time": integer, seconds, capped at 86400 (24h)

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/1f9785ef76b9e97f785dfa4b91876a19f3c20c8e.1777153011.git.g@b4.vu