This patch actually does quite a few things.  When looking to add
controller reset support, the organization modeled after rdma was
very fragmented. rdma duplicates the reset and teardown paths and does
different things to the block layer on the two paths. The code to build
up the controller is also duplicated between the initial creation and
the reset/error recovery paths. So I decided to make this sane.

I reorganized the controller creation and teardown so that there is a
connect path and a disconnect path.  Initial creation obviously uses
the connect path.  Controller teardown will use the disconnect path,
followed last access code. Controller reset will use the disconnect
path to stop operation, and then the connect path to re-establish
the controller.

Along the way, several things were fixed
- aens were not properly set up. They are allocated differently from
  the per-request structure on the blk queues.
- aens were oddly torn down. the prior patch corrected to abort, but
  we still need to dma unmap and free relative elements.
- missed a few ref counting points: in aen completion and on i/o's
  that fail
- controller initial create failure paths were still confused vs teardown
  before converting to ref counting vs after we convert to refcounting.
Signed-off-by: NJames Smart <james.smart@broadcom.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>