iavf: use generic power management

With the support of generic PM callbacks, drivers no longer need to use
legacy .suspend() and .resume() in which they had to maintain PCI states
changes and device's power state themselves. The required operations are
done by PCI core.

PCI drivers are not expected to invoke PCI helper functions like
pci_save/restore_state(), pci_enable/disable_device(),
pci_set_power_state(), etc. Their tasks are completed by PCI core itself.

Compile-tested only.

Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>