Add leds support on mainline devices

[Herrie82]

Is your feature request related to a problem? Please describe.
We have a nyx-modules for leds for hybris based devices, would be good to replicate for mainline since there is proper led support in kernels now.

We might want to bring back CoreNaviLeds in luna-sysmgr: webOS-ports/luna-sysmgr@f9973a3

Describe the solution you'd like
Replicate above for mainline. led can be enabled by setting brightness value. "echo 100 > brightness"

root@pinephonepro:/sys/class/leds# ls -l
lrwxrwxrwx 1 root root 0 Apr 28 2022 blue:indicator -> ../../devices/platform/leds/leds/blue:indicator
lrwxrwxrwx 1 root root 0 Apr 28 2022 green:indicator -> ../../devices/platform/leds/leds/green:indicator
lrwxrwxrwx 1 root root 0 Apr 28 2022 mmc2:: -> ../../devices/platform/fe330000.mmc/leds/mmc2::
lrwxrwxrwx 1 root root 0 Apr 28 2022 red:indicator -> ../../devices/platform/leds/leds/red:indicator
lrwxrwxrwx 1 root root 0 Apr 28 2022 white:flash -> ../../devices/platform/led-controller/leds/white:flash

Additional context
See also: https://source.puri.sm/Librem5/feedbackd/-/blob/main/src/fbd-ledctrl.c
https://source.puri.sm/Librem5/feedbackd/-/blob/main/src/fbd-dev-led-multicolor.c
https://source.puri.sm/Librem5/feedbackd/-/blob/main/src/fbd-dev-led.c
https://source.puri.sm/Librem5/feedbackd/-/blob/main/src/fbd-dev-leds.c
https://source.puri.sm/Librem5/feedbackd/-/blob/main/src/fbd-feedback-led.c

[Tofee]

I see there's already https://github.com/webOS-ports/nyx-modules/blob/webOS-ports/webOS-OSE/src/led_controller/led_controller.c , what's missing there?

[Herrie82]

I think that only does lcd backlight?