i2c: fsi: Add transfer implementation

Execute I2C transfers from the FSI-attached I2C master. Use polling
instead of interrupts as we have no hardware IRQ over FSI.

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>