dmaengine: stm32-mdma: enable descriptor_reuse

Enable descriptor reuse to allow client to resubmit already processed
descriptors in order to save descriptor creation time.

Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Link: https://lore.kernel.org/r/20200127085334.13163-6-amelie.delaunay@st.com


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