configs: imx8mn_beacon_fspi: Add config for booting from QSPI

The imx8mn-beacon SOM has a QSPI part on it connected to the
FlexSPI controller.  Add a defconfig option which supports
booting from the QSPI NOR flash instead of sd/mmc.

Signed-off-by: Adam Ford <aford173@gmail.com>
1 file changed