MAINTAINERS: add myself as MIPS guest cores co-maintainer

Add myself to the maintainer list for MIPS guest cores and update the status
from "Odd Fixes" to "Maintained".

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Acked-by: Aurelien Jarno <aurelien@aurel32.net>
Message-id: 1413459487-13658-1-git-send-email-leon.alrae@imgtec.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>