common/mlx5: fix shared memory region ranges allocation

common/mlx5: fix shared memory region ranges allocation

Memory regions (MRs) were allocated in one chunk of memory with a
mempool registration object. However, MRs can be reused among
different mempool registrations.

When the registration that allocated the MRs originally was
destroyed, the dangling pointers to the MRs could be left in other
registrations sharing these MRs.

Splitting the memory allocation of registration structure and MRs in
this commit solves this pointer reference issue.

Fixes: 690b2a88c2f7 ("common/mlx5: add mempool registration facilities")

Signed-off-by: Bing Zhao <bingz@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Reviewed-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>