Based on a patch from @grahamc on slack, tweaked so it works

Prior to this, the outcome was a machine that worked until the first
time you reboot it, and then it got stuck in the EFI shell requiring
manual intervention.

Mostly copied from c2.medium.x86 with tweaks after doing an
install (kernel modules, second serial port, cpu core count).

Am I doing this right?  How do we get packet.net to pick up the new
image(s)?

19.03

18.09 redux

18.09 has MLX enabled by default now