Establish some consistency with extension logging. Some extensions use another format:
display_alert "message" "${EXTENSION}" "info"
These were *not* adapted to this new schema.
- introduce hooks `grub_early_config`, `grub_pre_install` and `grub_late_config`
- what we see here is an extension that itself has hooks, that just works
- introduce extension `grub-with-dtb`, which
- enables `grub` extension
- requires `BOOT_FDT_FILE` to be set
- includes `/etc/armbian-grub-with-dtb` with `BOOT_FDT_FILE=` in the bsp-cli
- includes `/etc/kernel/postinst.d/armbian-grub-with-dtb` in the bsp-cli
- which reads the above and creates links for `/boot/armbian-dtb-<version>` when deploying deb's
- adds implementations of the hooks above to
- replace the distro's `10_linux` with our own `09_linux_with_dtb`
- which looks for `/boot/armbian-dtb-<version>`
- forcibly run `/etc/kernel/postinst.d/armbian-grub-with-dtb` during image build, since bsp-cli is installed after linux-image
- uefi-arm64: enable GRUB wallpaper by setting `UEFI_GRUB_TERMINAL=gfxterm`
- force GRUB_FONT so Ubuntu is not confused and gfxterm (incl wallpaper) finally works
