IB/CORE: sync the resouce access in fmr_pool

IB/CORE: sync the resouce access in fmr_pool

orabug: 25677461

There were some problem in the fmr_pool code that either was missing lock
protection or was using wrong lock when allocating/freeing/looking up resource
in the FMR pool.

Covering all above issues, the code turns out that every where we need lock
protection we need both the pool_lock and used_pool_lock. So this patch also
removes the used_pool_lock and keeps the pool lock and make the later sync
all the accesses.

Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Reviewed-by: Avinash Repaka <avinash.repaka@oracle.com>