qrb4210-rb2: add HDMI audio playback support

Merge series from Alexey Klimov <alexey.klimov@linaro.org>:

This series still keeps "qcom,qrb4210-rb2-sndcard" for sm8250 soundcard. As per
off the list discussion with Srini it was suggested to have it since in future it
may be required to add clocks, workarounds, quirks, model-specific things based on
this compatible. The same as for RB5 compatible in sm8250 snd driver.

This focuses on HDMI audio playback only hence there are no soundwire and dmic pins,
for instance. The work to enable playback via wcd+wsa8815 amplifier is in progress (it works)
and one of the routes is to merge such two patchsets together.

Link to prev series:
https://lore.kernel.org/linux-sound/20240628010715.438471-1-alexey.klimov@linaro.org/

Documentation/devicetree/bindings/sound/qcom,sm8250.yaml

@@ -30,6 +30,7 @@ properties:
           - qcom,apq8096-sndcard
           - qcom,qcm6490-idp-sndcard
           - qcom,qcs6490-rb3gen2-sndcard
+          - qcom,qrb4210-rb2-sndcard
           - qcom,qrb5165-rb5-sndcard
           - qcom,sc7180-qdsp6-sndcard
           - qcom,sc8280xp-sndcard

sound/soc/qcom/sm8250.c

@@ -174,6 +174,7 @@ static int sm8250_platform_probe(struct platform_device *pdev)
 
 static const struct of_device_id snd_sm8250_dt_match[] = {
 	{.compatible = "qcom,sm8250-sndcard"},
+	{.compatible = "qcom,qrb4210-rb2-sndcard"},
 	{.compatible = "qcom,qrb5165-rb5-sndcard"},
 	{}
 };