ARM: dts: sun8i: r40: Add I2C pinmux options

The R40 has five I2C controllers. Currently only I2C0 has its pinmux
option defined.

Add the options for the remaining four, and set them as the default,
since each controller has only one possible pinmux configuration.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>