ASoC: sunxi: sun4i-spdif: Implement IEC958 control

SPDIF core is capable of sending custom status.

Implement IEC958 control handling.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20211117194458.2249643-1-jernej.skrabec@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>