dma: enable mxs-dma for imx6q

enable the mxs-dma for imx6q.
Also remove the unused header file.

Signed-off-by: Huang Shijie <shijie8@gmail.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>