ASoC: imx-pcm-dma: DT support

This patch removes the NO_DT flag. The pdev pointer may have a proper
of_node with the dmas property, so we can use it to request DMA
channels.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Mark Brown <broonie@linaro.org>