dmaengine: sun4i: support module autoloading

MODULE_DEVICE_TABLE() is missing, so the module isn't auto-loading on
supported systems. This commit adds the missing line so it loads
automatically when building it as a module and running on a system
with the early sunxi DMA engine.

Signed-off-by: Emilio López <emilio.lopez@collabora.co.uk>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>