powerpc: Add I2C bus multiplexer node for B4 and T4240QDS

In both B4 and T4240QDS platform PCA9547 I2C bus multiplexer is used.
The sub-nodes are also reorganized according to right I2C topology.

Signed-off-by: Jia Hongtao <hongtao.jia@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>