ASoC: dt-bindings: Add support for Loongson audio card

The audio card uses loongson I2S controller present in
7axxx/2kxxx chips to transfer audio data.

On loongson platform, the chip has only one I2S controller.

Signed-off-by: Yingkun Meng <mengyingkun@loongson.cn>
Link: https://lore.kernel.org/r/20230614122659.3402788-1-mengyingkun@loongson.cn


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