ASoC: fsl: Drop formats limitation for imx-pcm-dma.c

Now ASoC core is getting the intersection of supported formats not only
from CPU and CODEC dai's but also from DMA's. However, there should be
no specific width limitation from SDMA side.

So drop it. Otherwise, we would only support S16_LE format for all i.MX
platforms.

Signed-off-by: Nicolin Chen <Guangyu.Chen@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>