samples: drivers spi_flash on the external NORof stm32h5 disco kit

Define the configuration to run the test on the external memory
xspi flash of the stm32h573i_dk disco kit in MemoryMapped Mode
Reading is done with memcopy and erase/write are aborting operation
to send the appropriate command

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