sky2: Do not use legacy PCI power management

The sky2 driver uses the legacy PCI power management, so it has to do
some PCI-specific things in its ->suspend() and ->resume() callbacks,
which isn't necessary and should better be done by the PCI
sybsystem-level power management code.  Moreover, it uses
device_set_wakeup_enable() incorrectly (that function should be
used when the WoL setting is changed rather than during suspend).

Convert sky2 to the new PCI power management framework and make it
let the PCI subsystem take care of all the PCI-specific aspects of
device handling during system power transitions.

Tested on a desktop machine with a Marvell 88E8056 PCI-E adapter.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>