arm64: dts: rockchip: Add soc-ctl-syscon to sdhci for rk3399

On rk3399 we'd like to be able to properly set corecfg registers in the
Arasan SDHCI component.  Specify the syscon to enable that.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>