Add a helper function to check a device's header type for PCI bridge or
CardBus bridge.

Requires: 326c1cda PCI: Rename pci_is_bridge() to pci_has_subordinate()
Signed-off-by: NYijing Wang <wangyijing@huawei.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>