dt-bindings: nvmem: Add Spreadtrum eFuse controller documentation

This patch adds the binding documentation for Spreadtrum eFuse controller.
Signed-off-by: Freeman Liu <freeman.liu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20191029114240.14905-7-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

+= Spreadtrum eFuse device tree bindings =
+
+Required properties:
+- compatible: Should be "sprd,ums312-efuse".
+- reg: Specify the address offset of efuse controller.
+- clock-names: Should be "enable".
+- clocks: The phandle and specifier referencing the controller's clock.
+- hwlocks: Reference to a phandle of a hwlock provider node.
+
+= Data cells =
+Are child nodes of eFuse, bindings of which as described in
+bindings/nvmem/nvmem.txt
+
+Example:
+
+	ap_efuse: efuse@32240000 {
+		compatible = "sprd,ums312-efuse";
+		reg = <0 0x32240000 0 0x10000>;
+		clock-names = "enable";
+		hwlocks = <&hwlock 8>;
+		clocks = <&aonapb_gate CLK_EFUSE_EB>;
+
+		/* Data cells */
+		thermal_calib: calib@10 {
+			reg = <0x10 0x2>;
+		};
+	};
+
+= Data consumers =
+Are device nodes which consume nvmem data cells.
+
+Example:
+
+	thermal {
+		...
+
+		nvmem-cells = <&thermal_calib>;
+		nvmem-cell-names = "calibration";
+	};