RFR: 8350325: [PPC64] ConvF2HFIdealizationTests timeouts on Power8

[David Linus Briemann]

Skip ConvF2HFIdealizationTests for Power8

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Commit messages:
 - switch skipped test to slow one
 - fix expression
 - skip ScalarFloat16OperationsTest for Power 8

Changes: https://git.openjdk.org/jdk/pull/23692/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23692&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350325
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23692.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23692/head:pull/23692

PR: https://git.openjdk.org/jdk/pull/23692