ASoC: jz4740: Use the generic dmaengine PCM driver

Now that there is a dmaengine driver for the jz4740 DMA core we can use the
generic dmaengine PCM driver. This allows us to remove the custom jz4740-pcm
code completely.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>