arm64: dts: rockchip: add spdif node to rk356x

This adds the spdif node to the rk356x device tree.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Link: https://lore.kernel.org/r/20211015111303.1365328-1-frattaroli.nicolas@gmail.com


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