ARM: mvebu: Add support for I2C controllers in Armada 370/XP

The Armada 370 and Armada XP have the same I2C controllers as previous
Marvell SoCs, so the existing mv64xxx-i2c driver works fine.

[Thomas Petazzoni: updated on top of other Armada 370/XP changes,
rephrased the commit log].
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>