i2c: some overdue driver removal

This patch contains the overdue removal of three I2C drivers.

[JD: In fact only i2c-ixp4xx can be removed at the moment, the other two
platforms don't implement the generic GPIO layer yet.]

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>