ROCKCHIP with MAX98357A/RT5514/DA7219 codecs on GRU boards

Required properties:
- compatible: "rockchip,rk3399-gru-sound"
- rockchip,cpu: The phandle of the Rockchip I2S controller that's
  connected to the codecs
- rockchip,codec: The phandle of the audio codecs

Optional properties:
- dmic-wakeup-delay-ms : specify delay time (ms) for DMIC ready.
  If this option is specified, which means it's required dmic need
  delay for DMIC to ready so that rt5514 can avoid recording before
  DMIC send valid data

Example:

sound {
	compatible = "rockchip,rk3399-gru-sound";
	rockchip,cpu = <&i2s0>;
	rockchip,codec = <&max98357a &rt5514 &da7219>;
	dmic-wakeup-delay-ms = <20>;
};