stmmac: pci: convert to use dev_pm_ops

Convert system PM callbacks to use dev_pm_ops. In addition remove the PCI calls
related to a power state since the bus code cares about this already.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>