arm64: dts: rockchip: generalize rk3399 #sound-dai-cells

The soc spdif and i2s controllers always only have one compontent, so
always require #sound-dai-cells to be 0. Therefore there is no need to
duplicate this property in individual boards.

So move them to rk3399.dtsi.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>