`bootc` is dependent on a specific EFI structure

In the case of `bootc install to-existing-root`, the existing root may have the entire /boot partition as a single vfat instead of a combination of a Linux and vfat volume.

This then breaks basically every post day-0 command which expects a certain directory structure in /boot.

Namely the availability of the symlinks which aren't possible in the vfat filesystem.