[jdk17u-dev] RFR: 8297445: PPC64: Represent Registers as values

[Martin Doerr]

Backport of [JDK-8297445](https://bugs.openjdk.org/browse/JDK-8297445). Fixes GCC11 build warnings ([JDK-8297426](https://bugs.openjdk.org/browse/JDK-8297426)).

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Commit messages:
 - Remove obsolete stuff.
 - 8297445: PPC64: Represent Registers as values

Changes: https://git.openjdk.org/jdk17u-dev/pull/2454/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2454&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297445
  Stats: 861 lines in 15 files changed: 163 ins; 466 del; 232 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2454.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2454/head:pull/2454

PR: https://git.openjdk.org/jdk17u-dev/pull/2454