mediatek: fix SPDX license identifier on local DTS files

The SPDX license identifier must be in the first line of a file,
unless there is a shebang (then it's the second line).

Fix this for the local files, do not care about the upstream patches.

While at it, update the identifiers where necessary.

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

target/linux/mediatek/dts/mt7622-bananapi-bpi-r64-rootdisk.dts

@@ -1,8 +1,7 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR MIT)
 /*
  * Copyright (c) 2018 MediaTek Inc.
  * Author: Ryder Lee <ryder.lee@mediatek.com>
- *
- * SPDX-License-Identifier: (GPL-2.0-only OR MIT)
  */
 
 /dts-v1/;