net/mlx5: EQ add/del CQ API

Add API to add/del CQ to/from EQs CQ table to be used in cq.c upon CQ
creation/destruction, as CQ table is now private to eq.c.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Gal Pressman <galp@mellanox.com>