net/mlx5: DR, Remove the buddy used_list

net/mlx5: DR, Remove the buddy used_list

No need to have the used_list - we don't need to keep track of the
used chunks, we only need to know the amount of used memory.

Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>