RFR: 8248191: [PPC64] Replace lxvd2x/stxvd2x with lxvx/stxvx for Power10

[Ziviani]

The pair lxvx/stxvx are more modern VSX instructions to load/store data.
These should benefit the Vector API because lxvd2x/stxvd2x may require
xxswapd, leading to a more difficult code generation.

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Commit messages:
 - 8248191: [PPC64] Replace lxvd2x/stxvd2x with lxvx/stxvx for Power10

Changes: https://git.openjdk.java.net/jdk/pull/1086/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1086&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248191
  Stats: 115 lines in 4 files changed: 87 ins; 0 del; 28 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1086.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1086/head:pull/1086

PR: https://git.openjdk.java.net/jdk/pull/1086