RFR(M): PPC64: improve array copy stubs by using vector instructions

[Gustavo Romero]

Hi Martin

Could you please host and review this webrev?

Summary:

* Add VSR registers to be used with VSX instruction set;
* Add VSX load/store instructions (lxvd2x/stxvd2x) to mass copy in
  the stub for disjoint short copy in order to improve it.

http://81.de.7a9f.ip4.static.sl-reverse.com./8154156/9/v4/

Thank you!

Best regards,
Gustavo