MAINTAINERS: Add myself as reviewer of ARM FSL/NXP

I would like to help reviewing FSL/NXP ARM architecture patches.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Olof Johansson <olof@lixom.net>