Update imx-sdma driver to adopt generic DMA device tree bindings.  It
calls of_dma_controller_register() with imx-sdma specific of_dma_xlate
to get the generic DMA device tree helper support.  The #dma-cells for
imx-sdma must be 3, which includes request ID, peripheral type and
priority.

The existing way of requesting channel, clients directly call
dma_request_channel(), still work there, and will be removed after
all imx-sdma clients get converted to generic DMA device tree helper.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>