CVE-2017-5754

BugLink: http://bugs.launchpad.net/bugs/1742772

We use the x86 'nopti' option because all the documenation on earth is
going to refer to that, and we can guess what users mean when they
specify that - they want to avoid any overhead due to Meltdown
mitigations.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>