i2c: mxs: Add basic support for i2c framework

This patch just converts the function prototypes used throughout
this driver to match those of the i2c framework. There is so far
no functional change. This patch does not do the deeper integration
of the framework bits.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Heiko Schocher <hs@denx.de>