leds: Add AAEON UP board LED driver

Add support for LEDs on AAEON UP boards. These leds are managed by the
onboard FPGA:
- UP boards: yellow, green, red
- UP Squared boards: blue, yellow, green, red

Based on the work done by Gary Wang <garywang@aaeon.com.tw>, largely
rewritten.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://lore.kernel.org/r/20241211-aaeon-up-board-pinctrl-support-v1-2-24719be27631@bootlin.com


Signed-off-by: Lee Jones <lee@kernel.org>