MAINTAINERS: imx: include drivers/firmware/imx path

Due to newly added IMX SCU firmware support, let's add
drivers/firmware/imx into maintainership.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

MAINTAINERS

@@ -1462,7 +1462,9 @@ F:	arch/arm/mach-mxs/
 F:	arch/arm/boot/dts/imx*
 F:	arch/arm/configs/imx*_defconfig
 F:	drivers/clk/imx/
+F:	drivers/firmware/imx/
 F:	drivers/soc/imx/
+F:	include/linux/firmware/imx/
 F:	include/soc/imx/
 
 ARM/FREESCALE VYBRID ARM ARCHITECTURE