xfs: enable ro-compat fs-verity flag

Finalize fs-verity integration in XFS by making kernel fs-verity
aware with ro-compat flag.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: add spaces]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>