dmaengine: imx-sdma: add terminated list for freed descriptor in worker

dmaengine: imx-sdma: add terminated list for freed descriptor in worker

Add terminated list for keeping descriptor so that it could be freed in
worker without any potential involving next descriptor raised up before
this descriptor freed, because vchan_get_all_descriptors get all
descriptors including the last terminated descriptor and the next
descriptor, hence, the next descriptor maybe freed unexpectly when it's
done in worker without this patch.
https://www.spinics.net/lists/dmaengine/msg23367.html

Change-Id: Iece434f55f3c6b5cf861fc23e4076fd4aa670ac4
Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Reported-by: Richard Leitner <richard.leitner@skidata.com>
(cherry picked from commit 24e30e721438600a496bcf1ae44cb4d7c93eafd8)