net: add dependency on fw class module to qlcnic and netxen_nic

netxen_nic and qlcnic driver depends on firmware_class module.

Signed-off-by: Anirban Chakraborty <anirban.chakraborty@qlogic.com>
Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>