PCI: Unhide the SMBus on the Asus P4P800-X

Unhide the SMBus on the Asus P4P800-X (and probably some other
models of the family.) This gives access to the memory module SPD
EEPROMs.

Thanks to Winbond for supporting the lm-sensors project with the
donation of this motherboard.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>