dt-bindings: iio: light: Add max44009

Adds device tree bindings for the max44009 light sensor.
Signed-off-by: Robert Eshleman <bobbyeshleman@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/light/max44009.txt

+* MAX44009 Ambient Light Sensor
+
+Required properties:
+
+- compatible: should be "maxim,max44009"
+- reg: the I2C address of the device (default is <0x4a>)
+
+Optional properties:
+
+- interrupts: interrupt mapping for GPIO IRQ. Should be configured with
+  IRQ_TYPE_EDGE_FALLING.
+
+Refer to interrupt-controller/interrupts.txt for generic interrupt client
+node bindings.
+
+Example:
+
+light-sensor@4a {
+	compatible = "maxim,max44009";
+	reg = <0x4a>;
+
+	interrupt-parent = <&gpio1>;
+	interrupts = <17 IRQ_TYPE_EDGE_FALLING>;
+};