This patch configures the I2C bus timing registers according
to information passed via DT. Currently, 100kHz and 400kHz
modes are supported.

The TIMING2 register value is wrong in the documentation for
i.MX28! This was found and fixed by:
  Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NWolfram Sang <w.sang@pengutronix.de>