Running arch-test doesn't list powerpcspe, though Qemu can support it.
Running the helper directly shows:

$ /usr/lib/arch-test/powerpcspe
qemu: uncaught target signal 4 (Illegal instruction) - core dumped
Illegal instruction (core dumped)

QEMU_CPU=e500v2 needs to be passed.

$ QEMU_CPU=e500v2 arch-test powerpcspe
works correctly.

Patch attached and MR pending
https://github.com/kilobyte/arch-test/pull/16