RFR: 8255129: [PPC64, s390] Check vector_size_supported and add VectorReinterpret node

[Martin Doerr]

match_rule_supported_vector on PPC64 and s390 need to check vector_size_supported.
In addition, an implementation for VectorReinterpret is needed. It can get implemented empty when using src = dst register. Note that these 2 platforms support only one vector size at a time, so there's no need for move between different sizes.

I'd like to clean up match_rule_supported, too. Cases for which we return true don't need to get checked explicitely because true is default. And we don't need to check SpecialString... flags because they are handled by "disabled_by_jvm_flags". So they can still get disabled (e.g. by jdk/bin/java -XX:-TieredCompilation -XX:-SpecialStringIndexOf -XX:+PrintCompilation -XX:+PrintInlining TestString|grep StringLatin1::indexOf).

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Commit messages:
 - 8255129: [PPC64, s390] Check vector_size_supported and add VectorReinterpret node

Changes: https://git.openjdk.java.net/jdk/pull/783/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=783&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255129
  Stats: 158 lines in 2 files changed: 29 ins; 56 del; 73 mod
  Patch: https://git.openjdk.java.net/jdk/pull/783.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/783/head:pull/783

PR: https://git.openjdk.java.net/jdk/pull/783