cxgb4: query firmware for QoS offload resources

QoS offload needs Ethernet Offload (ETHOFLD) resources present in the
NIC. These resources are shared with other ULDs. So, query firmware
for the available number of traffic classes, as well as, start and
end indices (EOTID) of the ETHOFLD region.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>