xfs: factor out a xfs_ilock_iocb helper

mainline inclusion
from mainline-v5.11-rc4
commit f50b8f47
category: bugfix
bugzilla: 187526,https://gitee.com/openeuler/kernel/issues/I4KIAO

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f50b8f475a2c70ae8309c16b6d4ecb305a4aa9d6



--------------------------------

Add a helper to factor out the nowait locking logical for the read/write
helpers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
Conflicts: fs/xfs/xfs_file.c
Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>