Function setup_dma

pub(crate) unsafe fn setup_dma(
    dma: &Dma1<'_>,
    dma_streams: &'static [Stream<'_, Dma1<'_>>; 8],
    usart3: &'static Usart<'_, Dma1<'_>>,
)

Helper function called during bring-up that configures DMA.