ARM: multi_v7_defconfig: Enable BCM283x

Enable the BCM2835/BCM2836 options required to boot Raspberry Pi.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Lee Jones <lee@kernel.org>
Cc: Olof Johansson <olof@lixom.net>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Eric Anholt <eric@anholt.net>