ROCKCHIP with DP via I2S

Required properties:
- compatible: "rockchip,cdndp-sound"
- rockchip,cpu: The phandle of the Rockchip I2S controller controller that's
  connected to the codec
- rockchip,codec: The phandle of the the DP encoder node

Example:

sound {
	compatible = "rockchip,cdndp-sound";
	rockchip,cpu = <&i2s2>;
	rockchip,codec = <&cdn_dp>;
};