ARM: dts: mvebu: Update with the new compatible string for mv64xxx-i2c

The mv64xxx-i2c embedded in the Armada XP have a new feature to
offload i2c transaction. This new version of the IP come also with
some errata. This lead to the introduction to a another compatible
string.

This commit split the i2c information into armada-370.dtsi and
armada-xp.dtsi. Most of the data remains the same and stay in the
common file Armada-370-xp.dtsi. With this new feature the size of the
registers are bigger for Armada XP and the new compatible string is
used.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>