ASoC: rockchip-max98090: Support usage with and without HDMI

Add one optional property "rockchip,hdmi-codec" to let user specify HDMI
device node in DTS so machine driver can find hdmi-codec device node for
HDMI codec DAI.

Use the presence of rockchip,audio-codec and rockchip,hdmi-codec to
specify the use case.

Use max98090 only : specify rockchip,audio-codec.
Use HDMI only: specify rockchip,hdmi-codec.
Use both max98090 and HDMI: specify rockchip,audio-codec and
rockchip,hdmi-codec.

Move these properties to optional because they are not needed for
HDMI-only use case.
"rockchip,audio-codec": The phandle of the MAX98090 audio codec
"rockchip,headset-codec": The phandle of Ext chip for jack detection
Signed-off-by: Cheng-Yi Chiang <cychiang@chromium.org>
Link: https://lore.kernel.org/r/20191028071930.145899-3-cychiang@chromium.orgSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip-max98090.txt

@@ -5,15 +5,38 @@ Required properties:
 - rockchip,model: The user-visible name of this sound complex
 - rockchip,i2s-controller: The phandle of the Rockchip I2S controller that's
   connected to the CODEC
-- rockchip,audio-codec: The phandle of the MAX98090 audio codec
-- rockchip,headset-codec: The phandle of Ext chip for jack detection
+
+Optional properties:
+- rockchip,audio-codec: The phandle of the MAX98090 audio codec.
+- rockchip,headset-codec: The phandle of Ext chip for jack detection. This is
+                          required if there is rockchip,audio-codec.
+- rockchip,hdmi-codec: The phandle of HDMI device for HDMI codec.
 
 Example:
 
+/* For max98090-only board. */
+sound {
+	compatible = "rockchip,rockchip-audio-max98090";
+	rockchip,model = "ROCKCHIP-I2S";
+	rockchip,i2s-controller = <&i2s>;
+	rockchip,audio-codec = <&max98090>;
+	rockchip,headset-codec = <&headsetcodec>;
+};
+
+/* For HDMI-only board. */
+sound {
+	compatible = "rockchip,rockchip-audio-max98090";
+	rockchip,model = "ROCKCHIP-I2S";
+	rockchip,i2s-controller = <&i2s>;
+	rockchip,hdmi-codec = <&hdmi>;
+};
+
+/* For max98090 plus HDMI board. */
 sound {
 	compatible = "rockchip,rockchip-audio-max98090";
 	rockchip,model = "ROCKCHIP-I2S";
 	rockchip,i2s-controller = <&i2s>;
 	rockchip,audio-codec = <&max98090>;
 	rockchip,headset-codec = <&headsetcodec>;
+	rockchip,hdmi-codec = <&hdmi>;
 };