dmaengine: omap-dma: control start/stop directly

Program the non-cyclic mode DMA start/stop directly, rather than via
arch/arm/plat-omap/dma.c.

Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>