documentation: Add nvmem bindings documentation

This patch add the bindings document of Amlogic eFuse driver.
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

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

+= Amlogic eFuse device tree bindings =
+
+Required properties:
+- compatible: should be "amlogic,meson-gxbb-efuse"
+
+= Data cells =
+Are child nodes of eFuse, bindings of which as described in
+bindings/nvmem/nvmem.txt
+
+Example:
+
+	efuse: efuse {
+		compatible = "amlogic,meson-gxbb-efuse";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		sn: sn@14 {
+			reg = <0x14 0x10>;
+		};
+
+		eth_mac: eth_mac@34 {
+			reg = <0x34 0x10>;
+		};
+
+		bid: bid@46 {
+			reg = <0x46 0x30>;
+		};
+	};
+
+= Data consumers =
+Are device nodes which consume nvmem data cells.
+
+For example:
+
+	eth_mac {
+		...
+		nvmem-cells = <&eth_mac>;
+		nvmem-cell-names = "eth_mac";
+	};