common/mlx5: add mempool registration facilities

common/mlx5: add mempool registration facilities

Add internal API to register mempools, that is, to create memory
regions (MR) for their memory and store them in a separate database.
Implementation deals with multi-process, so that class drivers don't
need to. Each protection domain has its own database. Memory regions
can be shared within a database if they represent a single hugepage
covering one or more mempools entirely.

Add internal API to lookup an MR key for an address that belongs
to a known mempool. It is a responsibility of a class driver
to extract the mempool from an mbuf.

Signed-off-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>