RFR: 8332603: [PPC64] Improve itable_stub [v3]

[Amit Kumar]

> PPC Port similar to [JDK-8305959 (x86)](https://bugs.openjdk.org/browse/JDK-8305959) and [JDK-8307352(aarch64)](https://bugs.openjdk.org/browse/JDK-8307352)

Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:

  fixes the test case

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/19733/files
  - new: https://git.openjdk.org/jdk/pull/19733/files/57fbfe69..e7c60c71

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19733&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19733&range=01-02

  Stats: 6 lines in 1 file changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/19733.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19733/head:pull/19733

PR: https://git.openjdk.org/jdk/pull/19733