arm: mach-mvebu: convert to use mvebu-mbus driver

The changes needed to migrate the mach-mvebu (Armada 370 and Armada
XP) to the mvebu-mbus driver are fairly minimal, since not many
devices currently supported on those SoCs use address decoding
windows. The only one being the BootROM window, used to bring up
secondary CPUs.

However, this BootROM window needed for SMP brings an important
requirement: the mvebu-mbus driver must be initialized at the
->early_init() time, otherwise the BootROM window cannot be setup
early enough to be ready before the secondary CPUs are started.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>