RFR 8068977 Remove unused sun.misc.Unsafe prefetch intrinsic support

[Paul Sandoz]

Hi.

Please review this patch to remove prefetch read/write support:

http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8068977-hotspot-prefetch-intrinsic-cleanup/webrev/

This is covering a lot of areas and i could of easily fat fingered something and/or in my ignorance made a mistake, so please check carefully.

There is a corresponding patch for closed source that i will send internally.

Paul.