ar71xx: indicate upgrade using system LED

This enables the system LED to indicate a running firmware upgrade. This
pattern is used on most platforms provided by the generic base-files
package. ar71xx uses it's own implementation for the system-LED, where
the upgrade case is not yet implemented.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ar71xx/base-files/etc/diag.sh

@@ -575,6 +575,9 @@ set_state() {
 	preinit_regular)
 		status_led_blink_preinit_regular
 		;;
+	upgrade)
+		status_led_blink_preinit_regular
+		;;
 	done)
 		status_led_on
 		case $(board_name) in