ASoC: ep93xx: convert to use the DMA engine API

Now that we have the EP93xx DMA engine driver in place, we convert the ASoC
drivers (I2S, AC97 and PCM) to take advantage of this new API. There are no
functional changes.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>