lemp9: Add intel_idle.max_cstate=4 kernel parameter to fix freezes

[jackpot51]

This should fix pop-os/linux#45

[leviport]

This did not fix the freezing issue on the lemp9 we have in the lab, but I think it might be having a completely different issue. I can confirm that this PR makes system76-driver add the intel_idle.max_cstate=4 parameter on lemp9. Since we have accounts of that parameter fixing some lemp9's, I approve.

[t-lock]

@leviport Hi there. Can I assume that since this change was merged into the System76 driver package, that my having set it manually on my Lemp9 machine is fine to leave indefinitely?

Thanks for all your work and Merry Christmas 🎄

[jacobgkau]

@leviport Hi there. Can I assume that since this change was merged into the System76 driver package, that my having set it manually on my Lemp9 machine is fine to leave indefinitely?

Yes, the intention is to have that setting applied persistently on lemp9, whether it's via the driver (on Pop!_OS/Ubuntu-based distributions) or manually (on other distributions.)