MAINTAINERS: i.MX: Add board/freescale/*mx* path

Pass the board/freescale/*mx*/ path as files maintained by Stefano
Babic.

While this is not ideal and does not cover all the i.MX board cases,
it gives at least a better hint for the /scripts/get_maintainer.pl
tool.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>

MAINTAINERS

@@ -102,6 +102,7 @@ F:	arch/arm/include/asm/arch-imx/
 F:	arch/arm/include/asm/arch-mx*/
 F:	arch/arm/include/asm/arch-vf610/
 F:	arch/arm/include/asm/imx-common/
+F:	board/freescale/*mx*/
 
 ARM HISILICON
 M:	Peter Griffin <peter.griffin@linaro.org>