PPC64 VSX load/store instructions in stubs

[Gustavo Romero]

Hi Martin, Hi Volker

Currently VSX load/store instructions are not being used in PPC64 stubs,
particularly in arraycopy stubs inside generate_arraycopy_stubs() like,
but not limited to, generate_disjoint_{byte,short,int,long}_copy.

We can speed up mass copy using VSX (Vector-Scalar Extension) load/store
instruction in processors >= POWER8, the same way it's already done for
libc memcpy().

This is an initial patch just for jshort_disjoint_arraycopy() VSX vector
load/store:

http://81.de.7a9f.ip4.static.sl-reverse.com/202539/webrev

What are your thoughts on that? Is there any impediment to use VSX
instructions in OpenJDK at the moment?

Thank you.

Best regards,
Gustavo