bnx2: Add pci shutdown handler.

WoL and power state changes will now be done in the shutdown handler.
open/close/ethtool will no longer change the power state.  NVRAM
operations can now be permitted whether the device is up or down.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>