block: refactor blkpg_ioctl

mainline inclusion
from mainline-v5.8-rc1
commit fa9156ae
category: bugfix
bugzilla: 187268, https://gitee.com/openeuler/kernel/issues/I76JDY


CVE: NA

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Split each sub-command out into a separate helper, and move those helpers
to block/partitions/core.c instead of having a lot of partition
manipulation logic open coded in block/ioctl.c.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

conflicts:
	block/ioctl.c
	block/partition-generic.c
	include/linux/genhd.h
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>