arm64: dts: rockchip: add rk3399 dw-mmc resets

dw-mmc got its reset-properties specified, so add the softresets
for it on the rk3399.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>