Add helper functions to hide direct device flag operations:

    void pci_set_dev_assigned(struct pci_dev *dev);
    void pci_clear_dev_assigned(struct pci_dev *dev);
    bool pci_is_dev_assigned(struct pci_dev *dev);
Signed-off-by: NEthan Zhao <ethan.zhao@oracle.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>