i2c-piix4: Add ATI IXP200/300/400 support

This patch adds the ATI IXP southbridges support to i2c-piix4,
as it turned out those chips are compatible with it.

Signed-off-by: Rudolf Marek <r.marek@sh.cvut.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>