commit cb3d6759 upstream.

Check what firmware told us and enable/disable the barrier_nospec as
appropriate.

We err on the side of enabling the barrier, as it's no-op on older
systems, see the comment for more detail.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>