dt-bindings: mmc: Add support for rk3576 dw-mshc

dt-bindings: mmc: Add support for rk3576 dw-mshc

Add the compatible string for rockchip,rk3576-dw-mshc in its own new
block, for devices that have internal phase settings instead of external
clocks.

Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/010201919996f687-08c1988a-f588-46fa-ad82-023068c316ba-000000@eu-west-1.amazonses.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>