ARM: sun5i: dt: Add i2c muxing options

The i2c controller found on the Allwinner A13 has only one muxing option
available for each controller. Add them to the dtsi

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