dmaengine: ste_dma40: Supply full Device Tree parsing support

Using the new DMA DT bindings and API, we can register the DMA40 driver
as Device Tree capable. Now, when a client attempts to allocate a
channel using the DMA DT bindings via its own node, we are able to parse
the request and allocate a channel in the correct manner.

Cc: Dan Williams <djbw@fb.com>
Cc: Per Forlin <per.forlin@stericsson.com>
Cc: Rabin Vincent <rabin@rab.in>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: devicetree-discuss@lists.ozlabs.org
Acked-by: Vinod Koul <vinod.koul@intel.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>