i2c-ibm_iic: Register child nodes

This patch completes the conversion of the IBM IIC driver to an
of-platform driver.

It removes the index from the IBM IIC driver and makes it an unnumbered
driver. It then calls of_register_i2c_devices to properly register all
the child nodes in the DTS.

Signed-off-by: Sean MacLennan <smaclennan@pikatech.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>