dmaengine: axi-dmac: populate residue info for completed xfers

Starting with version 4.2.a, the AXI DMAC controller can report partial
transfers that have been issued.

This change implements computing DMA residue information for transfers,
based on that reported information.

The way this is done, is to dequeue the partial transfers from the FIFO of
partial transfers, store the partial length to the correct segment &
descriptor, and compute the residue before submitting the DMA cookie to the
DMA framework.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>