ASoC: omap-pcm: Allow only formats with 1, 2, and 4 byte physical size

sDMA support only transfer elements with 1, 2, and 4 byte physical
size. Initialize the pcm driver accordingly.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>