RFR: 8308143: [ppc] remove constant and add wrap-up for successor

[Amit Kumar]

This is cosmetic change, which adds simple range check logic and changes -1 to NOREG_ENCODING. I liked the changes for s390x so aligning PPC with the same.

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Commit messages:
 - changes -1 to NOREG_ENCODING and wraps successor()

Changes: https://git.openjdk.org/jdk/pull/13997/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13997&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308143
  Stats: 18 lines in 1 file changed: 4 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/13997.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13997/head:pull/13997

PR: https://git.openjdk.org/jdk/pull/13997