net/mlx5e: Use query_special_contexts cmd only once per mdev

Don't query the firmware so many times (num rqs * num wqes * wqe frags)
because it slows down linearly the interface creation time when the
product is larger. Do it only once per mdev and store the result in
mlx5e_param.

Due to helper function being called from different files, move it to
an appropriate location. Rename the function with a proper prefix and
add a small cleanup.

This fix applies only for legacy rq.

Fixes: 1b1e4868

 ("net/mlx5e: Use query_special_contexts for mkeys")
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Or Har-Toov <ohartoov@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>