PCI / PM: Use SMART_SUSPEND and LEAVE_SUSPENDED flags for PCIe ports

Make the PCIe port driver set DPM_FLAG_SMART_SUSPEND and
DPM_FLAG_LEAVE_SUSPENDED for the devices handled by it to benefit
from the opportunistic optimizations in the PCI layer enabled by
these flags.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>