iio: light: add DT bindings for Capella CM3605

This adds device tree bindings for the Capella Microsystems CM3605
ambient light sensor and short range proximity sensor.

Cc: devicetree@vger.kernel.org
Cc: Capella Microsystems <capellamicro@gmail.com>
Cc: Kevin Tsai <ktsai@capellamicro.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/light/cm3605.txt

+Capella Microsystems CM3605
+Ambient Light and Short Distance Proximity Sensor
+
+The CM3605 is an entirely analog part which however require quite a bit of
+software logic to interface a host operating system.
+
+This ALS and proximity sensor was one of the very first deployed in mobile
+handsets, notably it is used in the very first Nexus One Android phone from
+2010.
+
+Required properties:
+- compatible: must be: "capella,cm3605"
+- aset-gpios: GPIO line controlling the ASET line (drive low
+  to activate the ALS, should be flagged GPIO_ACTIVE_LOW)
+- interrupts: the IRQ line (such as a GPIO) that is connected to
+  the POUT (proximity sensor out) line. The edge detection must
+  be set to IRQ_TYPE_EDGE_BOTH so as to detect movements toward
+  and away from the proximity sensor.
+- io-channels: the ADC channel used for converting the voltage from
+  AOUT to a digital representation.
+- io-channel-names: must be "aout"
+
+Optional properties:
+- vdd-supply: regulator supplying VDD power to the component.
+- capella,aset-resistance-ohms: the sensitivity calibration resistance,
+  in Ohms. Valid values are: 50000, 100000, 300000 and 600000,
+  as these are the resistance values that we are supplied with
+  calibration curves for. If not supplied, 100 kOhm will be assumed
+  but it is strongly recommended to supply this.
+
+Example:
+
+cm3605 {
+	compatible = "capella,cm3605";
+	vdd-supply = <&foo_reg>;
+	aset-gpios = <&foo_gpio 1 GPIO_ACTIVE_LOW>;
+	capella,aset-resistance-ohms = <100000>;
+	interrupts = <1 IRQ_TYPE_EDGE_BOTH>;
+	io-channels = <&adc 0x01>;
+	io-channel-names = "aout";
+};