tulip: windbond-840: use generic power management

With stable 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.

Earlier, .resume() was invoking pci_enable_device(). Drivers should not
call PCI legacy helper functions, hence, it was removed. This should not
change the behavior of the device as this function is called by PCI core
if somehow pm_ops is not able to bind with the driver, else, required tasks
are managed by the core itself.

Compile-tested only.

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