nvme: rename the queue quiescing helpers

Naming the nvme helpers that wrap the block quiesce functionality
_start/_stop is rather confusing.  Switch to using the quiesce naming
used by the block layer instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>