dmaengine: dmatest: Add alignment parameter

Add parameter "alignment" to allow setting the address alignment
manually. Having the ability to configure address alignment from
user space adds new testing capabilities where different alignments can
be configured for testing without having to modify the dma device
alignment properties.

If configured, the alignment value will override the device alignment
property of the target device.

Signed-off-by: Seraj Alijan <seraj.alijan@sondrel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>