ofw_iicbus: Add method for manual setting of basic OFW parameters.

Some IIC multifunction devices may have multiple I2C addresses per chip, but
only the primary address is listed in the DT (e.g. MAX776200). In this case,
the sub-devices for the secondary addresses must be created manually with
fixed OFW parameters (node, name, compatibility string, IIC address).
Add a bus method to the ofw_iicbus interface that does this.

MFC after: 4 weeks