arm64: dts: rockchip: move rk3328 #sound-dai-cells to the soc dtsi

The rk3328 i2s and spdif controllers only ever have one output
connection, so as with all implementations of the rk3066 i2s
controllers we can keep the #sound-dai-cells in the main dtsi
instead of having it repeated in each board.

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