ARM: MM Enable building Feroceon L2 cache controller with ARCH_MVEBU

Kirkwood, which uses the Feroceon L2 cache controller will soon be
moving into mach-mvebu. Allow the cache controller to be built in this
situation.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>