dt-bindings: mmc: rockchip-dw-mshc: Add RK3588 compatible string

Add RK3588 compatible string for SD interface.

Co-developed-by: Shawn Lin <[e-mail]>
Signed-off-by: Shawn Lin <[e-mail]>
Signed-off-by: Lucas Tanure <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Heiko Stuebner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

Documentation/devicetree/bindings/mmc/rockchip-dw-mshc.yaml

···
               - rockchip,rk3368-dw-mshc
               - rockchip,rk3399-dw-mshc
               - rockchip,rk3568-dw-mshc
+              - rockchip,rk3588-dw-mshc
               - rockchip,rv1108-dw-mshc
               - rockchip,rv1126-dw-mshc
           - const: rockchip,rk3288-dw-mshc