Peppermint doesn't package kernels, we take them from Ubuntu 16.04 due to using their repository. Which means we(disclaimer: just a user here, not on the dev team, but it feels wrong to call PMOS "it") don't set the flags in the kernel.
You could try switching to the 4.8 kernel(HWE) and it might be included. It should soon be on by default(in PMOS 8 I assume) and you can ask for instructions if you want to do it manualy. HWE kernel (4.8 ) is supported by the Ubuntu kernel team.
Another option is using the mainline kernel, either by building it yourself(I don't recommend it) or from the kernel team alpha PPA. I think they're built with default settings, but I've never tried it