net/mlx5: Remove Q counter low level helper APIs

mlx5 core users are encouraged to use low level API (mlx5_cmd_exec)
without the need of helper functions, do this for q counters, remove
helper functions and call mlx5_cmd_exec directly from users.

This will help reduce the total amount of code and reduction of the
mlx5_core symbol table.

Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>