PCI / PM: Restore PME Enable if skipping wakeup setup

The wakeup_prepared PCI device flag is used for preventing subsequent
changes of PCI device wakeup settings in the same way (e.g. enabling
device wakeup twice in a row).

However, in some cases PME Enable may be updated by things like PCI
configuration space restoration in the meantime and it may need to be
set again even though the rest of the settings need not change, so
modify __pci_enable_wake() to do that when it is about to return
early.

Also, it is reasonable to expect that __pci_enable_wake() will always
clear PME Status when invoked to disable device wakeup, so make it do
so even if it is going to return early then.

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