regulator: max1586: add device-tree binding

Add max1586 regulator device-tree bindings documentation.
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/max1586-regulator.txt

+Maxim MAX1586 voltage regulator
+
+Required properties:
+- compatible: must be "maxim,max1586"
+- reg: I2C slave address, usually 0x14
+- v3-gain: integer specifying the V3 gain as per datasheet
+           (1 + R24/R25 + R24/185.5kOhm)
+- any required generic properties defined in regulator.txt
+
+Example:
+
+	i2c_master {
+		max1586@14 {
+			compatible = "maxim,max1586";
+			reg = <0x14>;
+			v3-gain = <1000000>;
+
+			regulators {
+				vcc_core: v3 {
+					regulator-name = "vcc_core";
+					regulator-compatible = "Output_V3";
+					regulator-min-microvolt = <1000000>;
+					regulator-max-microvolt = <1705000>;
+					regulator-always-on;
+				};
+			};
+		};
+	};