xfs: move kernel-specific superblock validation out of libxfs

xfs: move kernel-specific superblock validation out of libxfs

Source kernel commit: 3945ae03d822aa47584dd502ac024ae1e1eb9e2d

A couple of the superblock validation checks apply only to the kernel,
so move them to xfs_fc_fill_super before we add the needsrepair "feature",
which will prevent the kernel (but not xfsprogs) from mounting the
filesystem.  This also reduces the diff between kernel and userspace
libxfs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>