dts: bindings: dma controller supports mem2mem transfer

This checks if the DMA controller supports or not
the memory-to-memory transfers. For DMA Version1,
in the stm32f2xx, stm32f4xx, stm32f7xx series,
only DMA instance 2 is able to transfer mem-to-mem.
For other series, with DMA Version2, there is no such a limitation.

Signed-off-by: Francois Ramu <francois.ramu@st.com>