mempool: return 0 if area is too small on populate

Change rte_mempool_populate_iova() and rte_mempool_populate_virt() to
return 0 instead of -EINVAL when there is not enough room to store one
object, as it can be helpful for applications to distinguish this
specific case.

As this is an ABI change, use symbol versioning to preserve old
behavior for binary applications.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>