this adds the mediatek,led_source dts binding for
Asus RT-AC1200 devices' dtsi, for correct switch LED
behavior.
The dts-binding is introduced in commit:
65dc9e0980
Without this, we only have constantly very fast
blinking LEDs, which don't react on any traffic or
LAN events at all.
Signed-off-by: Tamas Balogh <tamasbalogh@hotmail.com>