PCI: add is_added flag to struct pci_dev

This lets us check if the device is really added to the driver core or
not, which is what we need when walking some of the bus lists.  The flag
is there in anticipation of getting rid of the other PCI device list,
which is what we used to check in this situation.

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>