net/mlx5: DR, Add memory statistics for domain object

Add counters for number of buddies that are currently in use per domain
per buddy type (STE, MODIFY-HEADER, MODIFY-PATTERN).

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