acpi-ca reports \_SB as a device

If you call AcpiGetType on \_SB, you get "device" and \_TZ gives "thermal". I don't think this is valid since these are system scopes, not devices and thermal zones.

I found this while testing a patch that scans the whole namespace (\) for devices. It turns out some systems put PCI link devices (PNP0C0F) in \, so we weren't probing them.

Nate