MAINTAINERS: Add i.MX team to all arm NXP platforms

i.MX team maintains layerscape as well, so add the whole
arch/arm/boot/dts/nxp directory as requested in [1].

[1] https://lore.kernel.org/all/Z+Vs+pHZs2fMP%2Fp3@lizhi-Precision-Tower-5810/

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>

Author: tq-steina

MAINTAINERS

@@ -2806,8 +2806,7 @@ S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/frank.li/linux.git
 F:	Documentation/devicetree/bindings/firmware/fsl*
 F:	Documentation/devicetree/bindings/firmware/nxp*
-F:	arch/arm/boot/dts/nxp/imx/
-F:	arch/arm/boot/dts/nxp/mxs/
+F:	arch/arm/boot/dts/nxp/
 F:	arch/arm64/boot/dts/freescale/
 X:	Documentation/devicetree/bindings/media/i2c/
 X:	arch/arm64/boot/dts/freescale/fsl-*