iio: adc: max1363: Add device tree binding documentation

Add the device tree documentation for all the supported parts. Mandatory
binding is the compatible string and the slave I2C address.

Optional properties can be used to specify the Vcc / Vref regulators, as
well as the IRQ line if available.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/max1363.txt

+* Maxim 1x3x/136x/116xx Analog to Digital Converter (ADC)
+
+The node for this driver must be a child node of a I2C controller, hence
+all mandatory properties for your controller must be specified. See directory:
+
+        Documentation/devicetree/bindings/i2c
+
+for more details.
+
+Required properties:
+  - compatible: Should be one of
+		"maxim,max1361"
+		"maxim,max1362"
+		"maxim,max1363"
+		"maxim,max1364"
+		"maxim,max1036"
+		"maxim,max1037"
+		"maxim,max1038"
+		"maxim,max1039"
+		"maxim,max1136"
+		"maxim,max1137"
+		"maxim,max1138"
+		"maxim,max1139"
+		"maxim,max1236"
+		"maxim,max1237"
+		"maxim,max1238"
+		"maxim,max1239"
+		"maxim,max11600"
+		"maxim,max11601"
+		"maxim,max11602"
+		"maxim,max11603"
+		"maxim,max11604"
+		"maxim,max11605"
+		"maxim,max11606"
+		"maxim,max11607"
+		"maxim,max11608"
+		"maxim,max11609"
+		"maxim,max11610"
+		"maxim,max11611"
+		"maxim,max11612"
+		"maxim,max11613"
+		"maxim,max11614"
+		"maxim,max11615"
+		"maxim,max11616"
+		"maxim,max11617"
+		"maxim,max11644"
+		"maxim,max11645"
+		"maxim,max11646"
+		"maxim,max11647"
+  - reg: Should contain the ADC I2C address
+
+Optional properties:
+  - vcc-supply: phandle to the regulator that provides power to the ADC.
+  - vref-supply: phandle to the regulator for ADC reference voltage.
+  - interrupts: IRQ line for the ADC. If not used the driver will use
+    polling.
+
+Example:
+adc: max11644@36 {
+	compatible = "maxim,max11644";
+	reg = <0x36>;
+	vref-supply = <&adc_vref>;
+};