dt-bindings Help for MCP ADCs

Signed-off-by: Soeren Andersen <san@rosetechnology.dk>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/mcp320x.txt

+* Microchip Analog to Digital Converter (ADC)
+
+The node for this driver must be a child node of a SPI controller, hence
+all mandatory properties described in
+
+        Documentation/devicetree/bindings/spi/spi-bus.txt
+
+must be specified.
+
+Required properties:
+	- compatible:  	Must be one of the following, depending on the
+			model:
+				"mcp3001"
+				"mcp3002"
+				"mcp3004"
+				"mcp3008"
+				"mcp3201"
+				"mcp3202"
+				"mcp3204"
+				"mcp3208"
+
+
+Examples:
+spi_controller {
+	mcp3x0x@0 {
+		compatible = "mcp3002";
+		reg = <0>;
+		spi-max-frequency = <1000000>;
+	};
+};