* rename .dts sources in overlay directory as *.dtso
* change "target +=" line in "dts-y +=" in overlay Makefile
* remove "always +=" line in overlay Makefile
* add .scr compilation support in kernel scripts/Makefile.lib
* patch kernel scripts/Makefile.dtbinst to avoid flattening overlay
directory
for the last two points, see
general-add-overlay-compilation-support.patch