mvebu: backport pending Turris Omnia LEDs improvements

mvebu: backport pending Turris Omnia LEDs improvements

It backports this patch series, which is currently on review:
https://lore.kernel.org/linux-leds/20220704105955.15474-1-kabel@kernel.org/T/#rb89a4ca5a836f17bdcc53d65549e0b1779bb6a18
It allows being able to configure LEDs in userspace.

This fixes issue described in Turris Build repository
https://gitlab.nic.cz/turris/os/build/-/issues/354
It happens in OpenWrt as well.

- Before
```
root@turris:/# ls /sys/class/leds/
ath10k-phy0  ath9k-phy1   mmc0::
```

 -After
```
root@turris:/# ls /sys/class/leds/
ath10k-phy0      rgb:indicator-2  rgb:lan-3        rgb:wlan-1
ath9k-phy1       rgb:lan-0        rgb:lan-4        rgb:wlan-2
mmc0::           rgb:lan-1        rgb:power        rgb:wlan-3
rgb:indicator-1  rgb:lan-2        rgb:wan
```

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(cherry picked from commit 049368b936988ce2c7f82c07367d168600fdbaa6)