doc: board: nxp: Add instructions to boot from QSPI

Add instructions to build and boot from  QSPI Flash

Signed-off-by: Mamta Shukla <mamta.shukla@leica-geosystems.com>
Signed-off-by: Thomas Haemmerle <thomas.haemmerle@leica-geosystems.com>
Tested-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
1 file changed