bnx2x: Implement PCI shutdown

Implement the PCI shutdown callback to support un-orderly shutdown, i.e.,
shutdowns in which the remove callback will not be called.

Due to the lack of this functionality, when an un-orderly shutdown occurred,
it was possible for wake-on-lan to remain disabled.

This is now fixed as the callback introduces the correct place in which
`system_state' can be queried and wake-on-lan be configured accordingly.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>