treewide: access device tree from userspace via /proc/

Access the device tree via /proc/device-tree/ is the documented way to
access the properties. Everything else might not work in future.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/lantiq/base-files/lib/functions/lantiq.sh

@@ -3,7 +3,7 @@
 lantiq_get_dt_led() {
 	local label
 	local ledpath
-	local basepath="/sys/firmware/devicetree/base"
+	local basepath="/proc/device-tree/base"
 	local nodepath="$basepath/aliases/led-$1"
 
 	[ -f "$nodepath" ] && ledpath=$(cat "$nodepath")