base-files: unify get_dt_led helper function

Lantiq and IPQ806X (which includes IPQ40XX) both define the
same custom function {ipq806x|lantiq}_get_dt_led.

This patch moves the function into the base-file package at
lib/functions/leds.sh to make it more accessible for other
targets as well.

Cc: Mathias Kresin <dev@kresin.me>
Cc: John Crispin <john@phrozen.org>
Cc: Hannu Nyman <hannu.nyman@iki.fi>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/lantiq/base-files/etc/diag.sh

@@ -2,14 +2,13 @@
 # Copyright (C) 2010-2015 OpenWrt.org
 
 . /lib/functions/leds.sh
-. /lib/functions/lantiq.sh
 
-boot="$(lantiq_get_dt_led boot)"
-failsafe="$(lantiq_get_dt_led failsafe)"
-running="$(lantiq_get_dt_led running)"
+boot="$(get_dt_led boot)"
+failsafe="$(get_dt_led failsafe)"
+running="$(get_dt_led running)"
 
 set_state() {
-    status_led="$boot"
+	status_led="$boot"
 
 	case "$1" in
 	preinit)