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

drivers/nvme/host/trace.c

@@ -139,3 +139,6 @@ const char *nvme_trace_disk_name(struct trace_seq *p, char *name)
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(nvme_trace_disk_name);
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(nvme_sq);