cxgb4: introduce SMT ops to prepare for SMAC rewrite support

Introduce SMT operations for allocating/removing entries from
SMAC table. Make TCAM filters use the SMT ops whenever SMAC rewrite
is required.

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>