net/mlx5: Add QP WQ support

A QP in ConnectX is a concatenation of RQ and SQ which share a QP-number
and work together.
Add support for allocating and managing the work-queue buffer for a QP, in
a similar way to how SQs and RQs are already supported.

Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>