I’ve made some really good progress in getting this all smoothed out and working well. I started with the upstream (AOSP) treble enabled implementation for db845c and added the older db820c over it, as well as added an automotive product.
I’ve also smoothed out the qcomlt-5.4 kernel and added what was needed for Android.
Mostly working, with the exception of USB Gadget (adb over USB) and the board’s analog audio features.
Build instructions are in the readme in this repository with pinned manifest;
Note: The kernel should work (with a proper defconfig) for debian as well. It cures all of the sporadic boot failure problems that all of the 4.14 kernels experienced to varying degrees.