osd: Add op_process_latency in perf counter

Fixes: #7167

Signed-off-by: Ray Lv <xiangyulv@gmail.com>
Merge pull request #1120 from xylv/wip-op-process-latency-squashed

osd: Add op_process_latency in perf counter

Reviewed-by: Sage Weil <sage@inktank.com>