i2c-pca-isa: Port to the new device driver model

Port the i2c-pca-isa driver to the new device driver model. I'm
using Rene Herman's new isa bus type, as it fits the needs nicely. One
benefit is that we can now give a proper parent to our i2c adapter.

Signed-off-by: Jean Delvare <khali@linux-fr.org>