leds: sun50i-a100: New driver for the A100 LED controller

Some Allwinner sunxi SoCs, starting with the A100, contain an LED
controller designed to drive RGB LED pixels. Add a driver for it using
the multicolor LED framework, and with LEDs defined in the device tree.

Acked-by: Guo Ren <guoren@kernel.org>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20231029212738.7871-3-samuel@sholland.org
Signed-off-by: Lee Jones <lee@kernel.org>