pinctrl: sunxi: add I2C3 mux for D1/T113-s3 (PG10/PG11)

pinctrl: sunxi: add I2C3 mux for D1/T113-s3 (PG10/PG11)

Boards based on the Allwinner D1/T113-s3, such as the
NetCube Systems Nagami, can expose a third I2C controller
on PG10/PG11. However, the sun20i_d1 pinctrl function table
lacked an entry for this mux.

Add the "i2c3" function with mux value 3 on PG10/PG11, allowing device
trees to enable the I2C3 controller.

Signed-off-by: Lukas Schmid <lukas.schmid@netcube.li>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>