ARM: dts: BCM5301X: Relicense Asus RT-AC87U file to the GPL 2.0+ / MIT

This matches licensing used by other BCM5301X files and is preferred as:
1) GPL 2.0+ makes is clearly compatible with Linux kernel
2) MIT is also permissive but preferred over ISC

This file were created and ever touched by a group of three people only:
Álvaro, Hauke and me.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm/boot/dts/bcm4709-asus-rt-ac87u.dts

@@ -1,20 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
 /*
  * Broadcom BCM470X / BCM5301X ARM platform code.
  * DTS for Asus RT-AC87U
  *
  * Copyright (C) 2015 Rafał Miłecki <zajec5@gmail.com>
- *
- * Permission to use, copy, modify, and/or distribute this software for any
- * purpose with or without fee is hereby granted, provided that the above
- * copyright notice and this permission notice appear in all copies.
- *
- * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
- * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
- * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
- * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
- * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
- * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
- * PERFORMANCE OF THIS SOFTWARE.
  */
 
 /dts-v1/;