arm64: zynqmp: Sync up license with mainline kernel

Mainline Linux kernel has adopted SPDX header license in a different
format then was used before. This patch is syncing it up.

Also update years in License text and remove Nathalie's email because it
is no longer valid.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/dts/zynqmp-clk.dtsi b/arch/arm/dts/zynqmp-clk.dtsi
index f6e83e1..45d84a6 100644
--- a/arch/arm/dts/zynqmp-clk.dtsi
+++ b/arch/arm/dts/zynqmp-clk.dtsi
@@ -1,11 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Clock specification for Xilinx ZynqMP
  *
- * (C) Copyright 2015, Xilinx, Inc.
+ * (C) Copyright 2015 - 2018, Xilinx, Inc.
  *
  * Michal Simek <michal.simek@xilinx.com>
- *
- * SPDX-License-Identifier:	GPL-2.0+
  */
 
 / {