lantiq: add led-upgrade alias for Fritz!Box 7412

This adds the led-upgrade alias for the AVM Fritz!Box 7412 to indicate a
running firmware upgrade.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 920abb9b5865fe0994a5c8115cde616dac63d5ae)

target/linux/lantiq/files-4.14/arch/mips/boot/dts/FRITZ7412.dts

@@ -18,6 +18,7 @@
 		led-boot = &power_green;
 		led-failsafe = &power_red;
 		led-running = &power_green;
+		led-upgrade = &power_red;
 
 		led-dsl = &info;
 		led-wifi = &wifi;