net/mlx5: Track the current number of completion EQs

In preparation to allocate completion EQs, add a counter to track the
number of completion EQs currently allocated. Store the maximum number
of EQs in max_comp_eqs variable.

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>