ASoC: dt-bindings: rockchip: Add compatible for rk3568 spdif

This patch adds compatible string for rk3568 spdif.
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1629800162-12824-5-git-send-email-sugar.zhang@rock-chips.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip-spdif.yaml

@@ -23,6 +23,7 @@ properties:
       - const: rockchip,rk3366-spdif
       - const: rockchip,rk3368-spdif
       - const: rockchip,rk3399-spdif
+      - const: rockchip,rk3568-spdif
       - items:
           - enum:
               - rockchip,rk3188-spdif