IB/mlx5: Expose CQE version to user-space

Per user context, work with CQE version that both the user-space
and the kernel support. Report this CQE version via the response of
the alloc_ucontext command.

Signed-off-by: Haggai Abramovsky <hagaya@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>