ASoC: samsung: Use ASoC dmaengine code where possible

Since all Exynos platforms have been converted to dmaengine and many of
the older platforms are in the process of conversion they do not need to
use the legacy s3c-dma APIs for DMA but can instead use the standard ASoC
dmaengine helpers. This both allows them to benefit from improvements
implemented in the generic code and supports multiplatform.

This patch includes some fixes from Padma for Exynos SoCs, her testing
was on a slightly earlier version of the patch due to unrelated breakage
preventing testing.

Signed-off-by: Mark Brown <broonie@linaro.org>
Tested By: Padmavathi Venna <padma.v@samsung.com>