Even though we initialise the platform part and the I2C controller
itself at boot time, we actually only access the bus on power down.
Meanwhile a rich OS might have configured the I2C pins differently or
even disabled the controller.
So repeat the platform setup and controller initialisation just before
we actually access the bus to power off the system. This is safe,
because at this point the rich OS should no longer be running.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>