target: use SPDX license identifiers on scripts

Use SPDX license tags to allow machines to check licenses.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/omap/image/gen_omap_sdcard_img.sh

@@ -1,11 +1,7 @@
 #!/bin/sh
-
+# SPDX-License-Identifier: GPL-2.0-only
 #
 # Copyright (C) 2013 OpenWrt.org
-#
-# This is free software, licensed under the GNU General Public License v2.
-# See /LICENSE for more information.
-#
 
 set -x
 [ $# -eq 5 ] || {