The device provides 6 channels which can be individually
turned off and on but groups of two channels share a common brightness
register.

Limitation: The GPIO to enable the device is not used yet.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230419111806.1100437-3-andreas@kemnade.info