P200/300/400 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: Greg Kroah-Hartman <gregkh@suse.de>
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