mx31: Add device definitions for the i.MX3x I2C controllers

The i.MX I2C driver has not yet been merged into mainline but it is
near to that and the device defintions don't depend directly on it
so we can add the devices now.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>