dmaengine: stm32_mdma: activate pack/unpack feature

If source and destination bus width differs pack/unpack MDMA
feature has to be activated for alignment.
This pack/unpack feature implies to have both source/destination address
and buffer length aligned on bus width.

Fixes: a4ffb13c

 ("dmaengine: Add STM32 MDMA driver")
Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>