xfs: Move fs/xfs/xfs_attr.h to fs/xfs/libxfs/xfs_attr.h

commit e2421f0b upstream.

This patch moves fs/xfs/xfs_attr.h to fs/xfs/libxfs/xfs_attr.h
since xfs_attr.c is in libxfs.  We will need these later in
xfsprogs.
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>