dmaengine: imx-sdma: Add a new DMATYPE for SAI

This patch simply adds a new DMATYPE for SAI which's included
in i.MX6 Solo X.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>