dt-bindings: nvmem: add description for UniPhier eFuse

Add uniphier-efuse dt-bindings documentation.

Signed-off-by: Keiji Hayashibara <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

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

···
+= UniPhier eFuse device tree bindings =
+
+This UniPhier eFuse must be under soc-glue.
+
+Required properties:
+- compatible: should be "socionext,uniphier-efuse"
+- reg: should contain the register location and length
+
+= Data cells =
+Are child nodes of efuse, bindings of which as described in
+bindings/nvmem/nvmem.txt
+
+Example:
+
+	soc-glue@5f900000 {
+		compatible = "socionext,uniphier-ld20-soc-glue-debug",
+			     "simple-mfd";
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges = <0x0 0x5f900000 0x2000>;
+
+		efuse@100 {
+			compatible = "socionext,uniphier-efuse";
+			reg = <0x100 0x28>;
+		};
+
+		efuse@200 {
+			compatible = "socionext,uniphier-efuse";
+			reg = <0x200 0x68>;
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			/* Data cells */
+			usb_mon: usb-mon@54 {
+				reg = <0x54 0xc>;
+			};
+		};
+	};
+
+= Data consumers =
+Are device nodes which consume nvmem data cells.
+
+Example:
+
+	usb {
+		...
+		nvmem-cells = <&usb_mon>;
+		nvmem-cell-names = "usb_mon";
+	}