fsi: Add I2C Responder SCOM driver

The I2CR has the capability to directly perform SCOM operations,
circumventing the need to drive the FSI2PIB engine. Add a new
driver to perform SCOM operations through the I2CR.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20230612195657.245125-15-eajames@linux.ibm.com
Signed-off-by: Joel Stanley <joel@jms.id.au>