MAINTAINERS: Update i.MX entry

Add two patterns:
 - Documentation/devicetree/bindings/firmware/fsl*
 - Documentation/devicetree/bindings/firmware/nxp*

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Author: MrVan

MAINTAINERS

@@ -2586,6 +2586,8 @@ L:	imx@lists.linux.dev
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/shawnguo/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/arm64/boot/dts/freescale/