ARM: mvebu: fix compatible strings of MBus on Armada 375 and Armada 38x

Due to the special handling of window 13 on Armada 375 and Armada 38x
(similar to Armada XP), the MBus hardware block is *not* compatible
with the one used on Armada 370. Using the Armada 370 compatible
string on Armada 375 and 38x will lead to a non-working device if
window 13 ends up being used.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>