ASoC: davinci-mcasp: Choose PCM driver based on configured DMA controller

Find the configured DMA controller by asking for a DMA channel in the
probe phase and releasing it right after. The controller device can be
found via the dma_chan struct and the controller is recognized from
the compatible property of its device node. The patch assumes EDMA if
there is no device node.

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