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>

target/linux/ramips/mt7621/base-files/etc/rc.button/lights_toggle

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+[[ "${ACTION}" = "released" ]] || exit 0
+
+. /lib/functions.sh
+
+case "$(board_name)" in
+tplink,ec330-g5u-v1)
+	led_light="/sys/class/gpio/led-light/value"
+	echo "$((!$(cat $led_light)))" > "$led_light"
+;;
+	*)
+;;
+esac
+
+return 0