ASoC: omap-pcm: Request the DMA channel differently when DT is involved

When booting with DT the platform_get_resource_byname() is not available to
get the DMA resource. In this case the DAI drivers will set the filter_data to
the name of the DMA and omap-pcm can use this to request the DMA channel.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>