async_memcpy: convert to dmaengine_unmap_data

Use the generic unmap object to unmap dma buffers.

Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Tomasz Figa <t.figa@samsung.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Reported-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
[bzolnier: add missing unmap->len initialization]
[bzolnier: fix whitespace damage]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
[djbw: add DMA_ENGINE=n support]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index e721a1c..54138b5 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -1009,7 +1009,7 @@
 	return -ENOMEM;
 }
 
-static struct dmaengine_unmap_data *
+struct dmaengine_unmap_data *
 dmaengine_get_unmap_data(struct device *dev, int nr, gfp_t flags)
 {
 	struct dmaengine_unmap_data *unmap;
@@ -1024,6 +1024,7 @@
 
 	return unmap;
 }
+EXPORT_SYMBOL(dmaengine_get_unmap_data);
 
 /**
  * dma_async_memcpy_pg_to_pg - offloaded copy from page to page