dmaengine: omap-dma: Handle cases when the channel is polled for completion

dmaengine: omap-dma: Handle cases when the channel is polled for completion

When a DMA client driver decides that it is not providing callback for
completion of a transfer (and/or does not set the DMA_PREP_INTERRUPT) but
it will poll the status of the transfer (in case of short memcpy for
example) we will not get interrupt for the completion of the transfer and
will not mark the transaction as done.
Check the channel enable bit in the CCR when the status is queried and if
the channel is no longer active, we call the omap_dma_callback() to handle
the transfer completion.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>