- 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