md: convert to blk_alloc_disk/blk_cleanup_disk

mainline inclusion
from mainline-v5.14-rc1
commit 0f1d2e06
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=0f1d2e0643c544df50dbc436da930201218fa1e2



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Convert the md driver to use the blk_alloc_disk and blk_cleanup_disk
helpers to simplify gendisk and request_queue allocation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-15-hch@lst.de


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

Conflict:
	drivers/md/md.c
	the merging order of commit ad3fc798 ("md: revert io
	stats accounting") is inconsistent.

Signed-off-by: Li Nan <linan122@huawei.com>