realtek/8139too: use generic power management

compile-tested only

With legacy PM hooks, it was the responsibility
of a driver to manage PCI states and also
device's power state. The generic approach is
to let PCI core handle the work.

PCI core passes "struct device*" as an argument
to the .suspend() and .resume() callbacks. As
these callabcks work with "struct net_device*",
extract it from "struct device*" using
dev_get_drv_data().

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