tulip: de2104x: 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.

Earlier, .suspend() and .resume() were invoking pci_disable_device()
and pci_enable_device() respectively to manage the device's power state.
With generic PM, it is no longer needed. The driver is expected to just
implement driver-specific operations and leave power transitions to PCI
core.

Compile-tested only.

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