dmaengine: zxdma: Fix data width bug

Align src and dst width to fix data alignment issue as
trailing single transaction that does not fill a full
burst require identical src/dst data width.
Burst length limitation can be addressed well too.

Signed-off-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>