fiemap: add a nosync option

fiemap: add a nosync option

io/fiemap adds FIEMAP_FLAG_SYNC by default. There are some test cases
where adding this flag might have an undesired side effect on the
results [1].

Add an option that does not pass FIEMAP_FLAG_SYNC flag.

[1] https://lore.kernel.org/linux-xfs/ca21b3c4-e1df-4ba7-8e9c-5d221337c86b@huaweicloud.com/

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>