net/mlx5: Implement single completion EQ create/destroy methods

Currently, create_comp_eqs() function handles the creation of all
completion EQs for all the vectors on driver load. While on driver
unload, destroy_comp_eqs() performs the equivalent job.

In preparation for dynamic EQ creation, replace create_comp_eqs() /
destroy_comp_eqs() with  create_comp_eq() / destroy_comp_eq() functions
which will receive a vector index and allocate/destroy an EQ for that
specific vector. Thus, allowing more flexibility in the management
of completion EQs.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>