dmaengine: axi-dmac: Add MODULE_DEVICE_TABLE()

Add MODULE_DEVICE_TABLE() for the axi-dmac driver. This allows the driver
to be loaded on demand when built as a module.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>