mx5: Add i2c to Freescale MX51 Babbage HW

This patch adds I2C functionality to the Freescale MX51 Babbage HW.
The patch adds device structures, i2c board slave device defines,
IOMUX pin defines, and clocks.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>