arm64: dts: imx8mp-evk: enable fspi nor on imx8mp evk

enable fspi nor on imx8mp evk dts

Reviewed-by: Frank Li <frank.li@nxp.com>
Signed-off-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>