PCI: Unhide the SMBus on the HP xw4100

Unhide the SMBus on the HP xw4100. This gives access to a hardware
monitoring chip (ADT7463) and to the memory module SPD EEPROMs. I
checked that ACPI wasn't accessing the SMBus, so it should be safe.

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