leds: rgb: mt6370: Add MediaTek MT6370 current sink type LED Indicator support

leds: rgb: mt6370: Add MediaTek MT6370 current sink type LED Indicator support

The MediaTek MT6370 is a highly-integrated smart power management IC,
which includes a single cell Li-Ion/Li-Polymer switching battery
charger, a USB Type-C & Power Delivery (PD) controller, dual
Flash LED current sources, a RGB LED driver, a backlight WLED driver,
a display bias driver and a general LDO for portable devices.

Add support for the MediaTek MT6370 Current Sink Type LED Indicator
driver. It can control four channels current-sink RGB LEDs with 3 modes:
constant current, PWM, and breath mode.

Co-developed-by: Alice Chen <alice_chen@richtek.com>
Signed-off-by: Alice Chen <alice_chen@richtek.com>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/1df93a583c3f508a7158b83b95857e9bce235e1b.1678430444.git.chiaen_wu@richtek.com