ARM: dt-bindings: add device tree bindings for Hi3519 sysctrl

Add device tree bindings for Hi3519 system controller.
Signed-off-by: Jiancheng Xue <xuejiancheng@huawei.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

Documentation/devicetree/bindings/arm/hisilicon/hi3519-sysctrl.txt

+* Hisilicon Hi3519 System Controller Block
+
+This bindings use the following binding:
+Documentation/devicetree/bindings/mfd/syscon.txt
+
+Required properties:
+- compatible: "hisilicon,hi3519-sysctrl".
+- reg: the register region of this block
+
+Examples:
+sysctrl: system-controller@12010000 {
+	compatible = "hisilicon,hi3519-sysctrl", "syscon";
+	reg = <0x12010000 0x1000>;
+};