Add a driver for controlling the RGB LED via Ubiquitis own "LEDBAR" LED
controller based on the Holtek HT32F52241 MCU.
This driver is initially used by the Ubiquiti UniFi 6 LR, however
judging from FCC pictures the MCU is also found on the U6-Mesh as well
as the U6-Extender.
Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit c9137e2ddf)
