ARM: dts: imx6qdl-sabre: change to use SPDX identifiers

Replace the license text with SPDX identifiers.

Avoid the following checkpatch warning:

arch/arm/boot/dts/imx6qdl-sabrelite.dtsi:1: warning: Missing or
 malformed SPDX-License-Identifier tag in line 1
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-sabrelite.dtsi

+// SPDX-License-Identifier: GPL-2.0 OR X11
 /*
  * Copyright 2011 Freescale Semiconductor, Inc.
  * Copyright 2011 Linaro Ltd.
  *
- * 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 free software; you can redistribute it and/or
- *     modify it under the terms of the GNU General Public License
- *     version 2 as published by the Free Software Foundation.
- *
- *     This file is distributed in the hope that it will be useful,
- *     but WITHOUT ANY WARRANTY; without even the implied warranty of
- *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *     GNU General Public License for more details.
- *
- * 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.
  */
 
 #include <dt-bindings/clock/imx6qdl-clock.h>