dmaengine: imx-sdma: add device tree probe support

It adds device tree probe support for imx-sdma driver.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Vinod Koul <vinod.koul@intel.com>