Without this "jedec,spi-nor" compatible property, probing of the SPI NOR
does not work on the NXP i.MX6ULL EVK. Fix this by adding this
compatible property to the DT.

Fixes: 7d77b850 ("ARM: dts: imx6ull: fix the imx6ull-14x14-evk configuration")
Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>