i2c: Add FSI-attached I2C master algorithm

Add register definitions for FSI-attached I2C master and functions to
access those registers over FSI. Add an FSI driver so that our I2C bus
is probed up during an FSI scan.

Signed-off-by: Eddie James <eajames@linux.vnet.ibm.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>