tests: drivers: spi loopback with DMA testing on stm32h743 nucleo

with this config, the testcase PASSED on the nucleo_h743zi
using DMA for SPI transfer (through DMAMUX request)
Connect pins D11 and D12 on the ARDUIno connector CN7

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