[U-Boot] mxc_i2c: add new i2c subsystem support

[Philippe Reynes]

Hi Heiko,

The mxc_i2c driver use the legacy framework. I plan to
move this driver to new i2c subsystem (CONFIG_SYS_I2C).
Is someone already working on this task ?

If no, I propose to only add new i2c subsystem (and not
remove old i2c framework). We could remove the mxc i2c
legacy support when all the board using this driver will
be updated. What do you think about it ?

Regards,
Philippe