arm: dts: armada-385-turris-omnia: use SPDX-License-Identifier

Follow the recent trend for the license description, and also fix the
wrongly stated X11 to MIT.

As already pointed on the DT ML, the X11 license text [1] is explicitly
for the X Consortium and has a couple of extra clauses. The MIT
license text [2] is actually what the current DT files claim.

[1] https://spdx.org/licenses/X11.html
[2] https://spdx.org/licenses/MIT.html

Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Acked-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

arch/arm/boot/dts/armada-385-turris-omnia.dts

+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
 /*
  * Device Tree file for the Turris Omnia
  *
  * Copyright (C) 2016 Uwe Kleine-König <uwe@kleine-koenig.org>
  * Copyright (C) 2016 Tomas Hlavacek <tmshlvkc@gmail.com>
  *
- * This file is dual-licensed: you can use it either under the terms
- * of the GPL or the X11 license, at your option. Note that this dual
- * licensing only applies to this file, and not this project as a
- * whole.
- *
- *  a) This file is licensed under the terms of the GNU General Public
- *     License version 2.  This program is licensed "as is" without
- *     any warranty of any kind, whether express or implied.
- *
- * Or, alternatively,
- *
- *  b) Permission is hereby granted, free of charge, to any person
- *     obtaining a copy of this software and associated documentation
- *     files (the "Software"), to deal in the Software without
- *     restriction, including without limitation the rights to use,
- *     copy, modify, merge, publish, distribute, sublicense, and/or
- *     sell copies of the Software, and to permit persons to whom the
- *     Software is furnished to do so, subject to the following
- *     conditions:
- *
- *     The above copyright notice and this permission notice shall be
- *     included in all copies or substantial portions of the Software.
- *
- *     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- *     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
- *     OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
- *     NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
- *     HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
- *     WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
- *     FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
- *     OTHER DEALINGS IN THE SOFTWARE.
- */
-
-/*
  * Schematic available at https://www.turris.cz/doc/_media/rtrom01-schema.pdf
  */