dmaengine: stm32-dma: direct mode support through device tree

Direct mode or FIFO mode is computed by stm32-dma driver. Add a way for
the user to force direct mode, by setting bit 2 in the bitfield value
specifying DMA features in the device tree.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Link: https://lore.kernel.org/r/20200422102904.1448-3-amelie.delaunay@st.com


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