ARM: at91: fix GPLv2 wording

During the submission of these new sama5d4 files, the GPL notice mentioned the
device tree as a library, which is not really accurate.
Fix all these library mentions to reflect the fact that it's actually just a
file.
Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91-sama5d4ek.dts

@@ -9,12 +9,12 @@
  * licensing only applies to this file, and not this project as a
  * whole.
  *
- *  a) This library is free software; you can redistribute it and/or
+ *  a) This file is free software; you can redistribute it and/or
  *     modify it under the terms of the GNU General Public License as
  *     published by the Free Software Foundation; either version 2 of the
  *     License, or (at your option) any later version.
  *
- *     This library is distributed in the hope that it will be useful,
+ *     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.

arch/arm/boot/dts/sama5d4.dtsi

@@ -9,12 +9,12 @@
  * licensing only applies to this file, and not this project as a
  * whole.
  *
- *  a) This library is free software; you can redistribute it and/or
+ *  a) This file is free software; you can redistribute it and/or
  *     modify it under the terms of the GNU General Public License as
  *     published by the Free Software Foundation; either version 2 of the
  *     License, or (at your option) any later version.
  *
- *     This library is distributed in the hope that it will be useful,
+ *     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.