PPC440EPx: Optionally enable second I2C bus

The option CONFIG_I2C_MULTI_BUS does not have any effect on Sequoia, the
PPC440EPx reference platform, because IIC1 is never enabled. Add Sequoia board
code to turn on IIC1 if CONFIG_I2C_MULTI_BUS is selected.

Signed-off-by: Mike Nuss <mike@terascala.com>
Cc: Stefan Roese <sr@denx.de>