ARM: config: Add mvebu_v5_defconfig

Now that there is both v5 and v7 systems in mach-mvebu, the
mvebu_defconfig is not sufficient, since these systems cannot be
combined. Add a v5 defconfig which is based on kirkwood_defconfig,
but purely DT.

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>