ARM: mvebu: Add support for I2C on OpenBlocks AX3-4

The OpenBlocks AX3-4 board, based on the Armada XP SoC, has an I2C
bus. This patch enables this bus and sets the clock frequency of the
bus.

[Thomas Petazzoni: updated with other changes on OpenBlocks, rephrased
commit log.]
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

arch/arm/boot/dts/armada-xp-openblocks-ax3-4.dts

@@ -104,5 +104,13 @@ ethernet@d0034000 {
 			phy = <&phy3>;
 			phy-mode = "sgmii";
 		};
+		i2c@d0011000 {
+			status = "okay";
+			clock-frequency = <400000>;
+		};
+		i2c@d0011100 {
+			status = "okay";
+			clock-frequency = <400000>;
+		};
 	};
 };