cxgb4: add ETHOFLD hardware queue support

Add support for configuring and managing ETHOFLD hardware queues.
Keep the queue count and MSI-X allocation scheme same as NIC queues.
ETHOFLD hardware queues are dynamically allocated/destroyed as
TC-MQPRIO Qdisc offload is enabled/disabled on the corresponding
interface, respectively.

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