ARM: add v7 multi-platform defconfig

Add a v7 defconfig enabling highbank, socfpga, mvebu, and vexpress
platforms and their drivers. Most other options are left to the default.

The existing individual platform defconfigs are kept for now as they are
a bit different. In some cases, the choices look pretty arbitrary and
just copied from other defconfigs.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Gregory Clement <gregory.clement@free-electrons.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>