Update buildroot image to 2021.08 release

Mostly version updates of system packages. Noticeably this bumps QEMU
version from 5.2.0 to 6.0.0 (used by kvm-unit-tests).

Tests still complete in roughly two minutes on my desktop.

Test: make test
Change-Id: I08de94d3679f0911796d8cf07758cd24e96b5e73
1 file changed
tree: 6ccc8b9ad8bc7142ecad0d00e35521939f0f8eba
  1. linux-aarch64/
  2. linux-x86/
  3. README