arm64: dts: marvell: use the proper I2C controller compatible string for 7K/8K

The I2C controller found in the Marvell Armada 7K/8K provides the
bridge/offloading features, so the Device Tree should use the
marvell,mv78230-i2c compatible string instead of marvell,mv64xxx-i2c.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>