dt-bindings: arm: hisilicon: add bindings for HiKey960 board

Add bindings for HiKey960 Board.
Signed-off-by: Guodong Xu <guodong.xu@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

Documentation/devicetree/bindings/arm/hisilicon/hisilicon.txt

@@ -4,6 +4,10 @@ Hi3660 SoC
 Required root node properties:
 	- compatible = "hisilicon,hi3660";
 
+HiKey960 Board
+Required root node properties:
+	- compatible = "hisilicon,hi3660-hikey960", "hisilicon,hi3660";
+
 Hi3798cv200 SoC
 Required root node properties:
 	- compatible = "hisilicon,hi3798cv200";