This is designed to automatically create all neccessary makefiles, including ones for prebuilt apk's and libs.
See the extract-files.sh.template for an example of what should be in your device tree's extract-files.sh
You will also need the following files to describe the props to be extracted.
All "prebuilt" files (apk's or lib's) must have a "-" in front of the name.
i.e. -vendor/lib/libtime_genoff.so
This will prevent them from going in the PRODUCT_COPY_FILES block and instead build a makefile to build them as a prebuilt and include them in PRODUCT_PACKAGES.
In your device tree: device-proprietary-files.txt - Lists all device specific files
If you have a common device tree that shares props amoung your device family, you will need: common-proprietary-files.txt - Lists all common files that are shared in the device family
Optionally you can also have: proprietary-files.txt - Lists files that are on all devices but need to be device specific