xfs: remove the kuid/kgid conversion wrappers

mainline inclusion
from mainline-v5.6-rc4
commit ba8adad5
category: bugfix
bugzilla: 185881
CVE: CVE-2021-4037

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ba8adad5d036733d240fa8a8f4d055f3d4490562



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Remove the XFS wrappers for converting from and to the kuid/kgid types.
Mostly this means switching to VFS i_{u,g}id_{read,write} helpers, but
in a few spots the calls to the conversion functions is open coded.
To match the use of sb->s_user_ns in the helpers and other file systems,
sb->s_user_ns is also used in the quota code.  The ACL code already does
the conversion in a grotty layering violation in the VFS xattr code,
so it keeps using init_user_ns for the identity mapping.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

conflicts:
fs/xfs/libxfs/xfs_inode_buf.c
fs/xfs/xfs_inode_item.c

Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>