RFR: 8327652: S390x: Implements SLP support [v3]

[Sidraya Jayagond]

> This PR Adds SIMD support on s390x.

Sidraya Jayagond has updated the pull request incrementally with one additional commit since the last revision:

  Add proper comments and cosmetic changes.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18162/files
  - new: https://git.openjdk.org/jdk/pull/18162/files/8bb4bc33..487c57db

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18162&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18162&range=01-02

  Stats: 64 lines in 2 files changed: 11 ins; 1 del; 52 mod
  Patch: https://git.openjdk.org/jdk/pull/18162.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18162/head:pull/18162

PR: https://git.openjdk.org/jdk/pull/18162