dmaengine: xilinx_dma: Introduce xilinx_dma_get_residue

Introduce a function that can calculate residues for IPs that support it:
AXI DMA and CDMA.

Signed-off-by: Nicholas Graumann <nick.graumann@gmail.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Link: https://lore.kernel.org/r/1571150904-3988-5-git-send-email-radhey.shyam.pandey@xilinx.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>