consolidate tagset / misc request_queue allocation

[Christoph Hellwig]

Hi all,

this series consolidates the allocation and freeing of the tagsets
and misc (non-I/O) requests queues over the various fabrics drivers.

Eventually PCIe and the apple controller driver should use these
helpers as well, but that will require some additional cleanups of
the request_queue lifetime first.

Diffstat:
 host/core.c   |  100 +++++++++++++++++++++++++++++++++++++++++
 host/fc.c     |  121 +++++++++++--------------------------------------
 host/nvme.h   |   16 +++---
 host/rdma.c   |  141 +++++++++++++++-------------------------------------------
 host/tcp.c    |  118 +++++++++---------------------------------------
 target/loop.c |   91 +++++++++----------------------------
 6 files changed, 220 insertions(+), 367 deletions(-)