Add HDMI Audio support

Merge series from Biju Das <[e-mail]>:

This patch series aims to add HDMI audio support for RZ/{G2L,G2LC,V2L}
SMARC EVKs.

Documentation/devicetree/bindings/sound/renesas,rz-ssi.yaml

···
   '#sound-dai-cells':
     const: 0
 
+  port:
+    $ref: audio-graph-port.yaml#/definitions/port-base
+    description: Connection to controller providing I2S signals
+
 required:
   - compatible
   - reg