ARM: mvebu: update defconfig with 3.7 changes

The split of 370 and XP into two Kconfig options and the multiplatform
kernel support has changed a few Kconfig symbols, so let's update the
mvebu_defconfig file with the latest changes.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>