ASoC: dt-bindings: add schema for rockchip SAI controllers

Rockchip introduced a new audio controller called the "Serial Audio
Interface", or "SAI" for short, on some of their newer SoCs. In
particular, this controller is used several times on the RK3576 SoC.

Add a schema for it, with only an RK3576 compatible for now. Other SoCs
may follow as mainline support for them lands.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250410-rk3576-sai-v2-5-c64608346be3@collabora.com


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