This has apparently been a TODO item stuck until finding out
whether efi and isohybrid conflict or not; it's been a *long*
time since this has been found out (no conflict) actually,
let's add isohybrid to all of the images as it's completely
free size-wise and efi to chromium image as it's the largest
base one (I don't think that adding any extra functionality
to the already overweight and full of potential and kinetic
security bugs "flash" flavour is a good idea as it would
promote its use among those who need EFI but not Flash).