dmaengine: xilinx: xdma: Prepare the introduction of cyclic transfers

In order to reduce and clarify the diff when introducing cyclic
transfers support, let's first prepare the driver a bit. There is no
functional change.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20231005160237.2804238-3-miquel.raynal@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>