arm64: dts: rockchip: add i2s nodes support for RK3368 SoCs

I2S of RK3368 SoCs keep same as RK3066 SoCs found on Rockchip,
add nodes to support them.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>