nvme-pci: trace SQ status on completions

Export the disk name, queue id, sq_head, sq_tail to a trace event in
completion handling.

Usage example:

cd /sys/kernel/debug/tracing/events/nvme/nvme_sq

echo 'disk=="nvme1n1"' > filter

echo 1 > enable

cat /sys/kernel/debug/tracing/trace_pipe

Signed-off-by: yupeng <yupeng0921@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <keith.busch@intel.com>
[hch: slight formatting tweaks, use standard nvme tracepoint
 conventions]
Signed-off-by: Christoph Hellwig <hch@lst.de>

wip