ramips/leds: use devicetree alias led_wlan

Similiar to the lantiq target use a dts alias to define the wlan led
instead of static mapping in /etc/board.d/01_leds. Reduce code
duplication.
A device tree must define the alias "led-wlan" similiar to "led-boot".

/ {
        aliases {
                led-wlan = &led_wlan;
        };

        [..]

        led_wlan: wlan {
            label = "tl-wr841n-v14:green:wlan";
            gpios = <&gpio1 9 GPIO_ACTIVE_LOW>;
        };
};

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

target/linux/ramips/base-files/etc/board.d/01_leds

@@ -1,5 +1,6 @@
 #!/bin/sh
 
+. /lib/functions/leds.sh
 . /lib/functions/uci-defaults.sh
 
 set_wifi_led() {
@@ -12,6 +13,9 @@ boardname="${board##*,}"
 
 board_config_update
 
+led_wlan="$(get_dt_led wlan)"
+[ -n "$led_wlan" ] && ucidef_set_led_wlan "wifi_led" "wifi" "$led_wlan" "phy0tpt"
+
 case $board in
 3g-6200n|\
 br-6475nd|\