net/mlx5: DR, Manage definers with refcounts

In many cases different actions will ask for the same definer format.
Instead of allocating new definer general object and running out of
definers, have an xarray of allocated definers and keep track of their
usage with refcounts: allocate a new definer only when there isn't
one with the same format already created, and destroy definer only
when its refcount runs down to zero.

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