dmaengine: sun6i: Set default maxburst size and bus width

Some DMA clients, as audio, don't set the maxburst size and bus width
on the memory side when starting DMA transfers.
This patch prevents such transfers to be aborted by providing system
default values to the lacking ones.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>