video/backlight: document sysfs interface
Corentin Chary authored
Date and KernelVersion may be wrong because the backlight
interface was introduced before git initial import.

Cc:Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
3c4c1b69