With cmwq, there's no reason to use dedicated rds_ib_fmr_wq - it's not
in the memory reclaim path and the maximum number of concurrent work
items is bound by the number of devices.  Drop it and use system_wq
instead.  This rds_ib_fmr_init/exit() noops.  Both removed.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andy Grover <andy.grover@oracle.com>