There is an updated pull request by CameronNemo against master on the void-packages repository

https://github.com/CameronNemo/void-packages rock64-uboot
https://github.com/void-linux/void-packages/pull/21198

Rock64 U-Boot Image
This image uses the latest upstream sources and no binary blobs.
I have tested the boot on my device.

A patch file from https://github.com/void-linux/void-packages/pull/21198.patch is attached