PCI: Avoid slot reset if bridge itself is broken

When checking to see if a PCI slot can safely be reset, we previously
checked to see if any of the children had their PCI_DEV_FLAGS_NO_BUS_RESET
flag set.

Some PCIe root port bridges do not behave well after a slot reset, and may
cause the device in the slot to become unusable.

Add a check for PCI_DEV_FLAGS_NO_BUS_RESET being set in the bridge device
to prevent the slot from being reset.

Signed-off-by: Jan Glauber <jglauber@cavium.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>