ramips: enable LED button for TP-Link EC330-G5u v1

The device already has LED push button (KEY_LIGHTS_TOGGLE)
and exported GPIO control "led-light". This commit adds
button handler script for switching on/off all device LEDs.

Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>