mmc: davinci_mmc: convert to DMA engine API

Removes use of the DaVinci EDMA private DMA API and replaces
it with use of the DMA engine API.

Signed-off-by: Matt Porter <mporter@ti.com>
Tested-by: Koen Kooi <koen@dominion.thruhere.net>
Signed-off-by: Chris Ball <cjb@laptop.org>