dt-bindings: dma: New directory for STM32 DMA controllers bindings

Gather the STM32 DMA controllers bindings under ./dma/stm32/.
Then fix reference to old path in spi/st,stm32-spi.yaml: update the dmas
property description by referring to all STM32 DMA controllers bindings.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20240531150712.2503554-2-amelie.delaunay@foss.st.com


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