ASoC: meson: axg-tdm: restrict formats depending on slot width

Restrict the formats possible on the TDM interface depending on the width
of the TDM slot and let dpcm merging do the rest.

Fixes: d60e4f1e ("ASoC: meson: add tdm interface driver")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>