PCI / PM: Simplify device wakeup settings code

After previous changes it is not necessary to distinguish between
device wakeup for run time and device wakeup from system sleep states
any more, so rework the PCI device wakeup settings code accordingly.

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