mempool: support non-EAL thread

mempool: support non-EAL thread

For non-EAL thread, bypass per lcore cache, directly use ring pool.
It allows using rte_mempool in either EAL thread or any user pthread.
As in non-EAL thread, it directly rely on rte_ring and it's none preemptive.
It doesn't suggest to run multi-pthread/cpu which compete the rte_mempool.
It will get bad performance and has critical risk if scheduling policy is RT.
Haven't found significant performance decrease by mempool_perf_test.

Signed-off-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>