MAINTAINERS: add i.MX8 DT path to i.MX architecture

Shawn agreed to take patches for the i.MX8 parts through his tree.
Signed-off-by: NLucas Stach <l.stach@pengutronix.de>
Reviewed-by: NDong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: NAbel Vesa <abel.vesa@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

MAINTAINERS

@@ -1521,6 +1521,7 @@ F:	arch/arm/mach-imx/
 F:	arch/arm/mach-mxs/
 F:	arch/arm/boot/dts/imx*
 F:	arch/arm/configs/imx*_defconfig
+F:	arch/arm64/boot/dts/freescale/imx*
 F:	drivers/clk/imx/
 F:	drivers/firmware/imx/
 F:	drivers/soc/imx/