tests/drivers/spi: loopback testing on the stm32u5x spi with DMA

Adds the dma transfer for the SPI loopback test
for the b_u585i_iot02a disco kit and nuceo_u575zi_q.
GPDMA1 is the DMA instance
Connect pins on the target board D11 <--> D12 of the CN13

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