- determinining if `/boot` is vfat is more complex than it looks;
- use a common function to unify across all scripts
- during image build, the kernel install is always done with a non-fat, non-mounted /boot
- use a special variable passed through the env so unified function can know ahead of time
- introduce `extra_apt_envs` param to `chroot_sdcard_apt_get()`; array with extra environment vars
- if vfat /boot:
- `linux-update-symlinks` is not called (Debian would just choke on this)
- don't even try to symlink Armbian stuff, move instead
- more/better logging board-side (unfortunately mixed in all the set -x debugs)
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