[11u] RFR 8244847: Linux/PPC: runtime/CompressedOops/CompressedClassPointers: smallHeapTest fails

[Reingruber, Richard]

Hi,

Please help review this XXS backport of JDK-8244847 to 11u.
 
Original bug (JDK16):
  https://bugs.openjdk.java.net/browse/JDK-8244847
  https://git.openjdk.java.net/jdk/commit/4a267f1b

11u webrev:
  http://cr.openjdk.java.net/~rrich/webrevs/8244847_11u_Linux_PPC__runtime_CompressedOops_CompressedClassPointers__smallHeapTest_fails/webrev.0/
 
Adaptations:

  In both codelines, JDK16 and JDK11u, the fix reuses code for AARCH64 to search for a
  free address block below 32g that can be used for a zerobased compressed class
  space also on PPC64.
  
  In JDK16 the method Metaspace::reserve_address_space_for_compressed_classes() holds that code.
  In JDK11u it is the method Metaspace::allocate_metaspace_compressed_klass_ptrs().

  The test (CompressedClassPointers.java) is not changed because it's not disabled in 11u.

Testing:

CI testing @SAP: JCK and JTREG, also in Xcomp mode, SPECjvm2008, SPECjbb2015, Renaissance Suite,
SAP specific tests with fastdebug and release builds on all platforms
 
Thanks, Richard.