ASoC: spdif: Add S32_LE support for S/PDIF dummy codec drivers

AIO on UniPhier can output S/PDIF where no codec is needed.
This patch adds S32_LE support for dummy codec drivers.

If one S/PDIF controller has its own limitation, its CPU DAI driver should
set the supported format by its own circumstance, since the soc-pcm driver
will use the intersection of cpu_dai's formats and codec_dai's formats.

Signed-off-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Signed-off-by: Mark Brown <broonie@kernel.org>