dmaengine: zynqmp_dma: refine dma descriptor locking

The descriptor lists are locked for the entire tasklet that completes
the descriptors. This is not necessary, because the lock actually only
protects the descriptor lists.

Make the spin lock more fine-grained and only protect functions that
actually operate on the descriptor lists. This decreases the time when
the lock is held.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Link: https://lore.kernel.org/r/20210826094742.1302009-7-m.tretter@pengutronix.de


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