RFR: 8290082: [PPC64] ZGC C2 load barrier stub needs to preserve vector registers [v3]

[Martin Doerr]

> Preserve volatile vector registers in ZGC C2 load barrier stub.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  Update SOE spec for VSR regs. Add comment to register_ppc.hpp

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9453/files
  - new: https://git.openjdk.org/jdk/pull/9453/files/bb0513c1..2d8fa980

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9453&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9453&range=01-02

  Stats: 40 lines in 2 files changed: 4 ins; 0 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/9453.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9453/head:pull/9453

PR: https://git.openjdk.org/jdk/pull/9453