dt-bindings: display: bridge: nxp,tda998x: Convert to json-schema

Convert the NXP TDA998x HDMI transmitter Device Tree binding
documentation to json-schema.

Add missing "#sound-dai-cells" property.
Add ports hierarchy, as an alternative to port.
Drop pinctrl properties, as they do not belong here.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1224e757ec958f8b29ec66e783a7ee805c339d84.1663165552.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>