mlxsw: spectrum: Add support for counters on TCAM entries

Add support for packets and byte statistics on TCAM entries. The counters
are allocated from the generic flow counters pool.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>