- Autopatcher was commiting atrocities to the upstream DTs that are so
carefully hand-crafted, by simply rewriting everything, or trying to be
smart and failing at it (`incremental: true`)
- Instead, add `add-only: true` mode, where we simply only ever add to the
end of the Makefile, adding each new .dts and optionally the `subdir-y`
for overlays
- without incremental: true:
- we replace the DT Makefile based on *.dts at the DT directory after all patching/copying is done
- overlay target is added if overlays present
- with incremental: true:
- we parse the Makefile, parse the DTs being built, and only add .dts's we have added from 'dt' directory
- overlays target are not added; we assume smth else already added them
