dt-bindings: maxbotix,mb1232: Add MaxBotix i2c ultrasonic rangers

Add doc for dt binding maxbotix,mb1232. This binding is for MaxBotix
I2CXL-MaxSonar ultrasonic rangers which share a common i2c interface.
Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/proximity/maxbotix,mb1232.txt

+* MaxBotix I2CXL-MaxSonar ultrasonic distance sensor of type  mb1202,
+  mb1212, mb1222, mb1232, mb1242, mb7040 or mb7137 using the i2c interface
+  for ranging
+
+Required properties:
+ - compatible:		"maxbotix,mb1202",
+			"maxbotix,mb1212",
+			"maxbotix,mb1222",
+			"maxbotix,mb1232",
+			"maxbotix,mb1242",
+			"maxbotix,mb7040" or
+			"maxbotix,mb7137"
+
+ - reg:			i2c address of the device, see also i2c/i2c.txt
+
+Optional properties:
+ - interrupts:		Interrupt used to announce the preceding reading
+			request has finished and that data is available.
+			If no interrupt is specified the device driver
+			falls back to wait a fixed amount of time until
+			data can be retrieved.
+
+Example:
+proximity@70 {
+	compatible = "maxbotix,mb1232";
+	reg = <0x70>;
+	interrupt-parent = <&gpio2>;
+	interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
+};