ARM: sunxi: dt: Add i2c controller nodes to the DTSI

The Allwinner A10 and A13 both have 3 i2c controller embedded.
Add those to the common sunxi dtsi.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Tomasz Figa <tomasz.figa@gmail.com>