blk-mq: add the blk_mq_alloc_disk APIs

mainline inclusion
from mainline-v5.14-rc1
commit b461dfc4
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I81XCK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b461dfc49eb6fbabc60b9dad476e787ada56b7b4



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Add a new API to allocate a gendisk including the request_queue for use
with blk-mq based drivers.  This is to avoid boilerplate code in drivers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210602065345.355274-4-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>
conflict:
  include/linux/blk-mq.h
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
Signed-off-by: Li Nan <linan122@huawei.com>
(cherry picked from commit b10c31af)