Adapt the skge driver to the reworked PCI PM

* Use device_set_wakeup_enable() and friends as needed
* Remove an open-coded reference to the standard PCI PM registers
* Use pci_prepare_to_sleep() and pci_back_from_sleep() in the
  ->suspend() and ->resume() callbacks
* Use the observation that it is sufficient to call pci_enable_wake()
  once, unless it fails

Tested on Asus L5D (Yukon-Lite rev 7).

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>