ASoC: atmel-pcm: use generic dmaengine framework

Align atmel pcm to use ASoC generic dmaengine framework

DMA is fully device tree based

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>