RFR: 8348678: [PPC64] C2: unaligned vector load/store is ok

[Richard Reingruber]

This pr changes `Matcher::misaligned_vectors_ok`  to return `true` on PPC64 for better vectorization during `SuperWord`.
IR checking of the corresponding test `TestCastX2NotProcessedIGVN.java` is also enabled.

Tested with `TestCastX2NotProcessedIGVN.java`

The change passed our CI testing:
Tier 1-4 of hotspot and jdk. All of langtools and jaxp. Renaissance Suite and SAP specific tests.
Testing was done on the main platforms and also on Linux/PPC64le and AIX.

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

Commit messages:
 - Copyright year
 - misaligned_vectors_ok -> true
 - Check IR of TestCastX2NotProcessedIGVN::test2 also on ppc

Changes: https://git.openjdk.org/jdk/pull/23318/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23318&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348678
  Stats: 8 lines in 2 files changed: 2 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/23318.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23318/head:pull/23318

PR: https://git.openjdk.org/jdk/pull/23318