ASoC: dt-bindings: Add Rockchip RK3308 internal audio codec

Add device tree bindings document for the internal audio codec of the
Rockchip RK3308 SoC.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://msgid.link/r/20240305-rk3308-audio-codec-v4-2-312acdbe628f@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>