amd-xgbe: Convert to generic power management

Use dev_pm_ops structure to call generic suspend() and resume() callbacks.

Drivers should avoid saving device register and/or change power states
using PCI helper functions. With the generic approach, all these are handled
by PCI core.

Compile-tested only.

Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>