RFR: Generational ShenandoahGC on PPC64

[Martin Doerr]

PPC64 code for Generational ShenandoahGC.

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Commit messages:
 - Generational ShenandoahGC on PPC64

Changes: https://git.openjdk.java.net/shenandoah/pull/118/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=118&range=00
  Stats: 99 lines in 3 files changed: 92 ins; 2 del; 5 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/118.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/118/head:pull/118

PR: https://git.openjdk.java.net/shenandoah/pull/118