PCI PM: Register power state of devices during initialization

Use the observation that the power state of a PCI device can be
loaded into its pci_dev structure as soon as pci_pm_init() is run for
it and make that happen.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>