PCI/PM: Resume subordinate bus in bus type callbacks

Calling pci_resume_bus() on the secondary bus from pci_power_up() as it is
done now is questionable, because it depends on the mandatory bridge
power-up delays that are only covered by the PCI bus type PM callbacks.

For this reason, move the subordinate bus resume to those callbacks too and
use the observation that if a bridge is being powered-up during resume from
system-wide suspend, it may be still desirable to runtime-resume its
subordinate bus after completing the system-wide transition (in case the
resume of the devices on that bus is skipped during it).

Link: https://lore.kernel.org/r/3190097.aeNJFYEL58@kreacher


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>