DT: iio: adc: Add CC_10001 binding documentation

Add the devicetree binding document for Cosmic Circuits 10001 ADC device.
Reviewed-by: Andrew Bresticker <abrestic@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Phani Movva <Phani.Movva@imgtec.com>
Signed-off-by: Naidu Tellapati <Naidu.Tellapati@imgtec.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/cc10001_adc.txt

+* Cosmic Circuits - Analog to Digital Converter (CC-10001-ADC)
+
+Required properties:
+  - compatible: Should be "cosmic,10001-adc"
+  - reg: Should contain adc registers location and length.
+  - clock-names: Should contain "adc".
+  - clocks: Should contain a clock specifier for each entry in clock-names
+  - vref-supply: The regulator supply ADC reference voltage.
+
+Optional properties:
+  - adc-reserved-channels: Bitmask of reserved channels,
+    i.e. channels that cannot be used by the OS.
+
+Example:
+adc: adc@18101600 {
+	compatible = "cosmic,10001-adc";
+	reg = <0x18101600 0x24>;
+	adc-reserved-channels = <0x2>;
+	clocks = <&adc_clk>;
+	clock-names = "adc";
+	vref-supply = <&reg_1v8>;
+};