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

https://github.com/the-antz/void-packages pbp-dkms
https://github.com/void-linux/void-packages/pull/25882

pinebookpro-kernel: add missing header files
The missing vdso header files prevented dkms from building zfs (and
probably other modules).

They're also included in the upstream 5.8 package https://github.com/void-linux/void-packages/blob/6d11ea5f69d561753a77854017e660a9deb8080d/srcpkgs/linux5.8/template#L182

I successfully cross compiled it on ppc64le (compiles successfully, result untested) and native on aarch64 (compiles successfully, result seems to work fine).
I'm currently building it on aarch64-musl but I'm not sure if that's relevant for a kernel package.

A patch file from https://github.com/void-linux/void-packages/pull/25882.patch is attached