With board files, all I2C busses run at 400KHz. Fix the device-tree
to be consistent with this. It's possible this is incorrect, but at
least it keeps the board files and device-tree consistent.

Also, disable any I2C controllers that the board files don't register,
also for consistency.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>