nvmem: rockchip-efuse: describe the usage of eFuse

This patch add the bindings document of rockchip eFuse driver.

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: ZhengShunQian <zhengsq@rock-chips.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/nvmem/rockchip-efuse.txt

+= Rockchip eFuse device tree bindings =
+
+Required properties:
+- compatible: Should be "rockchip,rockchip-efuse"
+- reg: Should contain the registers location and exact eFuse size
+- clocks: Should be the clock id of eFuse
+- clock-names: Should be "pclk_efuse"
+
+= Data cells =
+Are child nodes of eFuse, bindings of which as described in
+bindings/nvmem/nvmem.txt
+
+Example:
+
+	efuse: efuse@ffb40000 {
+		compatible = "rockchip,rockchip-efuse";
+		reg = <0xffb40000 0x20>;
+		#address-cells = <1>;
+		#size-cells = <1>;
+		clocks = <&cru PCLK_EFUSE256>;
+		clock-names = "pclk_efuse";
+
+		/* Data cells */
+		cpu_leakage: cpu_leakage {
+			reg = <0x17 0x1>;
+		};
+	};
+
+= Data consumers =
+Are device nodes which consume nvmem data cells.
+
+Example:
+
+	cpu_leakage {
+		...
+		nvmem-cells = <&cpu_leakage>;
+		nvmem-cell-names = "cpu_leakage";
+	};