i2c: piix4: Register SPDs

The piix4 I2C bus can carry SPDs, register them if present.
Only look on bus 0, as this is where the SPDs seem to be located.

Only the first 8 slots are supported. If the system has more,
then these will not be visible.

The AUX bus can not be probed as on some platforms it reports all
devices present and all reads return "0".
This would allow the ee1004 to be probed incorrectly.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>