arm: mvebu: x240: Use i2c-gpio instead of built in controller

There is an Errata with the built-in I2C controller where various I2C
hardware errors cause a complete lockup of the CPU (which eventually
results in an watchdog reset).

Put the I2C MPP pins into GPIO mode and use the i2c-gpio driver instead.
This uses a bit-banged implementation of an I2C controller and avoids
triggering the Errata.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>