dmaengine: stm32-dma3: prevent pack/unpack thanks to DT configuration

dmaengine: stm32-dma3: prevent pack/unpack thanks to DT configuration

When source data width/burst and destination data width/burst are
different, data are packed or unpacked in DMA3 channel FIFO, using
CxTR1.PAM.
Data are pushed out from DMA3 channel FIFO when the destination burst
length (= data width * burst) is reached.
If the transfer is stopped before CxBR1.BNDT = 0, and if some bytes are
packed/unpacked in the DMA3 channel FIFO, these bytes are lost.
Indeed, DMA3 channel FIFO has no flush capability, only reset.
To avoid potential bytes lost, pack/unpack must be prevented by setting
memory data width/burst equal to peripheral data width/burst.
Memory accesses will be penalized. But it is the only way to avoid bytes
lost.

Prevent pack/unpack feature can be activated by setting bit 16 of DMA3
Transfer requirements bitfield (tr_conf) in device tree.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20241016-dma3-mp25-updates-v3-2-8311fe6f228d@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>