ARM: sun6i: Enable the I2C controllers

The A31 has 4 I2C controllers that are the same than the one in the
other Allwinner SoCs, except for the fact that they are asserted in
reset by the reset unit.

Add these i2c controllers to the DTSI.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>