RFR(S): 8196565: AIX: Clean up os::javaTimeNanos according to AIX/PASE specification

[Langer, Christoph]

Hi,

please review a fix for the os::javaTimeNanos method on AIX.

It implements the information we got from the AIX documentation and from the IBM folks regarding the behavior of mread_real_time on Pase.

Bug: https://bugs.openjdk.java.net/browse/JDK-8196565
Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8196565.0/

Thanks & Best regards
Christoph