VSX instructions were added in POWER ISA V2.06 (POWER7), but it requires data to be word-aligned. Such requirement was removed in ISA V2.07B (POWER8).
Since current memcpy/bcopy optimization relies on VSX instructions handling misalignment transparently, and kernel doesn't currently implement an alignment error handler, we should restrict this to ISA V2.07 onwards.
SIGBUS on stxvd2x instruction was reproduced in POWER7+ CPU.