Function setup_dma

pub(crate) unsafe fn setup_dma(
    dma: &Dma2<'_>,
    dma_streams: &'static [Stream<'static, Dma2<'_>>; 8],
    usart1: &'static Usart<'_, Dma2<'_>>,
)

Helper function called during bring-up that configures DMA.