critnib: add a reference counter and critnib_release()

Add a reference counter and critnib_release() function.

The following 4 functions:
- critnib_remove(),
- critnib_get(),
- critnib_find_le() and
- critnib_find()

returns a reference (void *ref) to the key,
that MUST be released by calling critnib_release()
when the returned value is no longer used
and can be freed using the cb_free_leaf() callback.

Fixes: oneapi-src#1233

Signed-off-by: Lukasz Dorau <[email protected]>

Author: ldorau