dt-bindings: iio: light: add vcnl4000 devicetree bindings

Document the vishay VCNL4000 devicetree bindings.
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/light/vcnl4000.txt

+VISHAY VCNL4000 -  Ambient Light and proximity sensor
+
+This driver supports the VCNL4000/10/20 and VCNL4200 chips
+
+Required properties:
+
+	-compatible: must be one of :
+        vishay,vcnl4000
+        vishay,vcnl4010
+        vishay,vcnl4020
+        vishay,vcnl4200
+
+	-reg: I2C address of the sensor, should be one from below based on the model:
+        0x13
+        0x51
+
+Example:
+
+light-sensor@51 {
+	compatible = "vishay,vcnl4200";
+	reg = <0x51>;
+};