ARM: edma: Add function to manually trigger an EDMA channel

Manual trigger for events missed as a result of splitting a
scatter gather list and DMA'ing it in batches. Add a helper
function to trigger a channel incase any such events are missed.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>