blk-throttle: Split the service queue

blk-throttle: Split the service queue

This patch splits throtl_service_queue->nr_queued into "nr_queued_bps" and
"nr_queued_iops", allowing separate accounting of BPS and IOPS queued bios.
This prepares for future changes that need to check whether the BPS or IOPS
queues are empty.

To facilitate updating the number of IOs in the BPS and IOPS queues, the
addition logic will be moved from throtl_add_bio_tg() to
throtl_qnode_add_bio(), and similarly, the removal logic will be moved from
tg_dispatch_one_bio() to throtl_pop_queued().

And introduce sq_queued() to calculate the total sum of sq->nr_queued.

Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Zizhi Wo <wozizhi@huaweicloud.com>
Link: https://lore.kernel.org/r/20250506020935.655574-7-wozizhi@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>