net: axienet: Factor out TX descriptor chain cleanup

[ Upstream commit ab365c3393664f32116aa22fe322cb04a93fab31 ]

Factor out the code that cleans up a number of connected TX descriptors,
as we will need it to properly roll back a failed _xmit() call.
There are subtle differences between cleaning up a successfully sent
chain (unknown number of involved descriptors, total data size needed)
and a chain that was about to set up (number of descriptors known), so
cater for those variations with some extra parameters.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 9ff2f816e2aa ("net: axienet: Fix register defines comment description")
Signed-off-by: Sasha Levin <sashal@kernel.org>