RFR: 8353500: [s390x] Intrinsify Unsafe::setMemory

[Amit Kumar]

Unsafe::setMemory intrinsic implementation for s390x. 

Will update benchmark:

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Commit messages:
 - s390: unsafe::setMemory Port

Changes: https://git.openjdk.org/jdk/pull/24480/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24480&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353500
  Stats: 132 lines in 2 files changed: 128 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/24480.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24480/head:pull/24480

PR: https://git.openjdk.org/jdk/pull/24480