ALSA: move dmaengine implementation from ASoC to ALSA core

For the PXA DMA rework, we need the generic dmaengine implementation
that currently lives in sound/soc for standalone (non-ASoC) AC'97
support.

Move it to sound/core, and rename the Kconfig symbol.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>