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

[Baesken, Matthias]

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