Add support for assigning DMA channels from a device tree.

[je: remove channel sub-node parsing, dynamic channel creation on xlate]
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NJoachim Eastwood <manabian@gmail.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>