nvme: split nvme_uninit_ctrl into stop and uninit

Usually before we teardown the controller we want to:
1. complete/cancel any ctrl inflight works
2. remove ctrl namespaces (only for removal though, resets
   shouldn't remove any namespaces).

but we do not want to destroy the controller device as
we might use it for logging during the teardown stage.

This patch adds nvme_start_ctrl() which queues inflight
controller works (aen, ns scan, queue start and keep-alive
if kato is set) and nvme_stop_ctrl() which cancels the works
namespace removal is left to the callers to handle.

Move nvme_uninit_ctrl after we are done with the
controller device.

Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index e0b8331..8f2a168 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -280,6 +280,8 @@ int nvme_shutdown_ctrl(struct nvme_ctrl *ctrl);
 int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
 		const struct nvme_ctrl_ops *ops, unsigned long quirks);
 void nvme_uninit_ctrl(struct nvme_ctrl *ctrl);
+void nvme_start_ctrl(struct nvme_ctrl *ctrl);
+void nvme_stop_ctrl(struct nvme_ctrl *ctrl);
 void nvme_put_ctrl(struct nvme_ctrl *ctrl);
 int nvme_init_identify(struct nvme_ctrl *ctrl);