ASoC: spdif: Add S20_3LE and S24_LE support for dummy codec drivers

Generally, S/PDIF supports 20bit and optional 24bit samples. Thus add these
two formats for the 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: Nicolin Chen <b42378@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>