blk-mq: move more logic into blk_mq_insert_requests

blk-mq: move more logic into blk_mq_insert_requests

Move all logic related to the direct insert (including the call to
blk_mq_run_hw_queue) into blk_mq_insert_requests to streamline the code
flow up a bit, and to allow marking blk_mq_try_issue_list_directly
static.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230413064057.707578-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>