drivers: dma: stm32u5 dma driver with two dma instances

Add a second instance of DMA to the stm32 dma driver from the DTS
That can be found in the stm32H5 serie, where 2 GPDMA with 8 channels
are available. Rebuilding with Macro.
Use the dma_channels property of the dedive tree to count the nb
of dma channels: 16 or 8 (like in stm32h5).

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