dmaengine: stm32-dma: add copy_align constraint

This patch adds copy_align property in accordance with hardware
restriction.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Link: https://lore.kernel.org/r/20200129153628.29329-7-amelie.delaunay@st.com


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