dt-bindings: Document the hi3660 reset bindings

Add DT bindings documentation for hi3660 SoC reset controller.
Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Documentation/devicetree/bindings/reset/hisilicon,hi3660-reset.txt

+Hisilicon System Reset Controller
+======================================
+
+Please also refer to reset.txt in this directory for common reset
+controller binding usage.
+
+The reset controller registers are part of the system-ctl block on
+hi3660 SoC.
+
+Required properties:
+- compatible: should be
+		 "hisilicon,hi3660-reset"
+- hisi,rst-syscon: phandle of the reset's syscon.
+- #reset-cells : Specifies the number of cells needed to encode a
+  reset source.  The type shall be a <u32> and the value shall be 2.
+
+	 Cell #1 : offset of the reset assert control
+	           register from the syscon register base
+		   offset + 4: deassert control register
+		   offset + 8: status control register
+	 Cell #2 : bit position of the reset in the reset control register
+
+Example:
+	iomcu: iomcu@ffd7e000 {
+		compatible = "hisilicon,hi3660-iomcu", "syscon";
+		reg = <0x0 0xffd7e000 0x0 0x1000>;
+	};
+
+	iomcu_rst: iomcu_rst_controller {
+		compatible = "hisilicon,hi3660-reset";
+		hisi,rst-syscon = <&iomcu>;
+		#reset-cells = <2>;
+	};
+
+Specifying reset lines connected to IP modules
+==============================================
+example:
+
+        i2c0: i2c@..... {
+                ...
+		resets = <&iomcu_rst 0x20 3>; /* offset: 0x20; bit: 3 */
+                ...
+        };