That the "repository" is for r7500v2.
I suspect the boot issue is related to how I got usb working. My repo has edits in qcom-ipq8064-r7500v2.dts tied to edits in qcom-ipq8064.dtsi to get usb working. I think you'll need to make "consistent" edits in qcom-ipq8065-r7800.dts (ty @slh) and qcom-ipq8064.dtsi (see @Ansuel's post above).
Note, my choice of labels and node names in these files is slightly different than what @Ansuel choose so be careful. I don't think it matters what label/names you choose as long as you are consistent; however, the "community" should decide soon to avoid this kind of confusion.
EDIT0: I did what I did because I can and I don't think many people care all that much what I'm doing... If I'm wrong about that, I'd be happy to update my repo for the r7800 as well. I don't have a r7800 so you'd have to test it.
EDIT1: I pushed a change to my repo for qcom-ipq8065-r7800.dts that you can try. For any R7800 user who might want to try, please search the thread for WARNING and read first. Test with caution. I believe a couple of other users have tried these changes on the r7800 but I don't know for certain. 4+ days up for me and no obvious issues.
Note, every time the kernel 4.19 patch is "refreshed" in the staging tree, I check for changes and update my repo using things like reset hard HEAD and reapply my patch set. Lastly, I'm currently not up to date with master due to the possible mac80211 issues mentioned above.