There's a closed pull request on the void-packages repository

rpi-kernel: make btrfs built-in module
https://github.com/void-linux/void-packages/pull/46522

Description:
This allows booting from btrfs partitions. Adds around 120kB to the uncompressed package size.

#### Testing the changes
- I tested the changes in this PR: **briefly**


- I built this PR locally for these architectures (if supported. mark crossbuilds):
  - aarch64-musl (Raspberry PI 3 Model A+)