ramips: TP-link archer A6/C6 device tree updates

ramips: TP-link archer A6/C6 device tree updates

Set correct GPIO (10) for the WPS button. This matches GPIO settings in
vendor GPL sources. Note that GPL sources also mention a USB indicator
LED (GPIO 13) but the device has neither an external USB port nor a USB LED.

In addition, prefixes (button-, led-) are added to relevant DT entries,
as well as color and function specifications for LEDs.

Closes: #13736
Reported-by: Waldemar Czabaj <kaball@wp.pl>
Signed-off-by: Rani Hod <rani.hod@gmail.com>
(added led mitigations for wifi leds)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>