ARM64: dts: gxbb: add i2c bus

Add nodes for i2c bus on gxbb based platforms.
On the OdroidC2 (I2C A) and P200 (I2C B), the pull-up resistor are
present directly on the board. This indicates that these pins are
dedicated to i2c.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>