media: dt-bindings: pwm-ir-tx: Add support for PWM IR Transmitter

Document the device tree bindings for the PWM IR Transmitter.
Signed-off-by: Sean Young <sean@mess.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/devicetree/bindings/leds/irled/pwm-ir-tx.txt

+Device tree bindings for IR LED connected through pwm pin which is used as
+remote controller transmitter.
+
+Required properties:
+	- compatible: should be "pwm-ir-tx".
+	- pwms : PWM property to point to the PWM device (phandle)/port (id)
+	  and to specify the period time to be used: <&phandle id period_ns>;
+
+Example:
+	irled {
+		compatible = "pwm-ir-tx";
+		pwms = <&pwm0 0 10000000>;
+	};