samples: drivers: quadspi flash of the stm32 boards

This enables the samples/drivers/spi_flash on quad-spi flash
to run on any stm32 target with external NOR quad flash.
The SPI_FLASH_MULTI_SECTOR_TEST test case is possible with
quadspi too.

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