iwlwifi: Convert to new PCI PM framework

Use the new PCI PM and let the PCI core code handle the PCI-specific
details of power transitions.

Based on similarly titled ath9k patch posted by Rafael J. Wysocki.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>