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/lib/functions/lantiq.sh

@@ -1,17 +1,5 @@
 #!/bin/sh
 
-lantiq_get_dt_led() {
-	local label
-	local ledpath
-	local basepath="/proc/device-tree"
-	local nodepath="$basepath/aliases/led-$1"
-
-	[ -f "$nodepath" ] && ledpath=$(cat "$nodepath")
-	[ -n "$ledpath" ] && label=$(cat "$basepath$ledpath/label")
-
-	echo "$label"
-}
-
 lantiq_is_vdsl_system() {
 	grep -qE "system type.*: (VR9|xRX200)" /proc/cpuinfo
 }