arm64: dts: rockchip: move i2s0 node from baseboard to SoM on rk3399-puma

The I2S definition is part of the SoM and therefore should be in
rk3399-puma.dtsi. Also correct the number of channels available.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>