dt-bindings: arm: hisilicon: Add binding for HiKey970 board

Add devicetree binding for HiKey970 board.
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

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

@@ -12,6 +12,10 @@ Hi3670 SoC
 Required root node properties:
 	- compatible = "hisilicon,hi3670";
 
+HiKey970 Board
+Required root node properties:
+	- compatible = "hisilicon,hi3670-hikey970", "hisilicon,hi3670";
+
 Hi3798cv200 SoC
 Required root node properties:
 	- compatible = "hisilicon,hi3798cv200";