arm: dts: keystone: Update devicetree header comments to sync with v6.3-rc6

Signed-off-by: Andrew Davis <afd@ti.com>
diff --git a/arch/arm/dts/keystone.dtsi b/arch/arm/dts/keystone.dtsi
index 9a2e1f6..31d0cee 100644
--- a/arch/arm/dts/keystone.dtsi
+++ b/arch/arm/dts/keystone.dtsi
@@ -1,9 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
- * Copyright 2013 Texas Instruments, Inc.
- *
- * This program 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.
+ * Copyright (C) 2013-2017 Texas Instruments Incorporated - http://www.ti.com/
  */
 
 #include <dt-bindings/interrupt-controller/arm-gic.h>