maintainership update for the Marvell Orion family of SOCs

While Lennert and I have moved our focus to other things, some people
picked up the slack on those platforms.  Let's empower them with a more
official status.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Cc: Lennert Buytenhek <kernel@wantstofly.org>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>