I think I'm right in thinking https://ukstore.qnap.com/catalog/product/view/id/215 is the machine you meant?
I've not yet built uboot myself, but these repos claim to have code for CN9130.
https://github.com/SolidRun/cn913x_build/
https://github.com/SolidRun/u-boot/tree/u-boot-v2019.10-marv...
https://solidrun.atlassian.net/wiki/spaces/developer/pages/3...
I think I'm right in thinking https://ukstore.qnap.com/catalog/product/view/id/215 is the machine you meant?