[media] dt: bindings: Add binding documentation for sunxi IR controller

Device-Tree bindings for SUNXI IR controller found in sunXi SoC family

Required properties:

- compatible	    : should be "allwinner,sun4i-a10-ir";

- clocks	    : list of clock specifiers, corresponding to

		      entries in clock-names property;

- clock-names	    : should contain "apb" and "ir" entries;

- interrupts	    : should contain IR IRQ number;

- reg		    : should contain IO map address for IR.

Optional properties:

- linux,rc-map-name : Remote control map name.

Example:

ir0: ir@01c21800 {

	compatible = "allwinner,sun4i-a10-ir";

	clocks = <&apb0_gates 6>, <&ir0_clk>;

	clock-names = "apb", "ir";

	interrupts = <0 5 1>;

	reg = <0x01C21800 0x40>;

	linux,rc-map-name = "rc-rc6-mce";

};