dmaengine: dmatest: honor alignment restriction for buffers

Existing implementation does not honor the alignment restrictions imposed
by the DMA engines. Allocate buffers with built in slack for honoring
alignment restrictions. Creating new arrays to hold the aligned pointers
and use those pointers for operations.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>