ARM: i.MX6: cm-fx6: refactor the I2C support code

Restructure/refactor the I2C support code and underlying devices code,
to localize the connected parts of the code and have better ability to
read/understand/debug the code.
Meanwhile, identify the potential and real bugs - add a comment.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>