blktrace: introduce 'blk_trace_{start,stop}' helper

Introduce 'blk_trace_{start,stop}' helper. No functional changed.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221019033602.752383-2-yebin@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>