mmc-host: move to dma_transfer_direction

fixup usage of dma direction by introducing dma_transfer_direction,
this patch moves mmc drivers to use new enum

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Chris Ball <cjb@laptop.org>
Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>