leds: Add mt6360 driver

Add MT6360 LED driver include 2-channel Flash LED with torch/strobe mode,
3-channel RGB LED support Register/Flash/Breath Mode, and 1-channel for
moonlight LED.

Signed-off-by: Gene Chen <gene_chen@richtek.com>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>