RFR: 8231751: on aix handle Power 9 in os::get_summary_cpu_info

Hello, please review this small change . It adds Power 9 handling to os::get_summary_cpu_info on AIX . Additionally some older macro definitions (like PV_6 ) are removed because they are present in sys/systemcfg.h on recent AIX versions ( 6.1 + ) . Bug/webrev : https://bugs.openjdk.java.net/browse/JDK-8231751 http://cr.openjdk.java.net/~mbaesken/webrevs/8231751.0/ Thanks, Matthias