arm64: dts: rockchip: Add SPDIF nodes to RK3588(s) device trees

arm64: dts: rockchip: Add SPDIF nodes to RK3588(s) device trees

RK3588s has four SPDIF transmitters, and the full RK3588 has six.
They are software compatible to RK3568 ones. Add respective nodes
to .dtsi files.

Adapted from vendor sources at [1] and [2], respectively

[1] https://github.com/rockchip-linux/kernel/blob/develop-5.10/arch/arm64/boot/dts/rockchip/rk3588s.dtsi
[2] https://github.com/rockchip-linux/kernel/blob/develop-5.10/arch/arm64/boot/dts/rockchip/rk3588.dtsi

Signed-off-by: Alexey Charkov <alchark@gmail.com>
Link: https://lore.kernel.org/r/20250120-rk3588-spdif-v1-2-1415f5871dc7@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>