dmaengine: add new enum dma_transfer_direction

This new enum removes usage of dma_data_direction for dma direction. The new
enum cleans tells the DMA direction and mode
This further paves way for merging the dmaengine _prep operations and also for
interleaved dma

Suggested-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>