MIPS: dts: mscc: Add i2c on ocelot

Ocelot has an i2c controller, add it. There is only one possible pinmux
configuration so add it as well.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20353/
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: linux-i2c@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Allan Nielsen <allan.nielsen@microchip.com>