RFR: 8332603: [ppc] Improve itable_stub

[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)

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

Commit messages:
 - ppc port

Changes: https://git.openjdk.org/jdk/pull/19733/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19733&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332603
  Stats: 154 lines in 3 files changed: 135 ins; 7 del; 12 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