blk-mq: Stop using pointers for blk_mq_tags bitmap tags

blk-mq: Stop using pointers for blk_mq_tags bitmap tags

Now that we use shared tags for shared sbitmap support, we don't require
the tags sbitmap pointers, so drop them.

This essentially reverts commit 1060241075a3 ("blk-mq: Use pointers for
blk_mq_tags bitmap tags").

Function blk_mq_init_bitmap_tags() is removed also, since it would be only
a wrappper for blk_mq_init_bitmaps().

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/1633429419-228500-14-git-send-email-john.garry@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>