RFR: 8354650: [PPC64] Try to reduce register definitions [v3]

[David Briemann]

> Defines the 32 vector registers and removes the 64 vector scalar register definitions. Reduces Mach registers from 398 to 270.

David Briemann has updated the pull request incrementally with one additional commit since the last revision:

  beautify code

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25828/files
  - new: https://git.openjdk.org/jdk/pull/25828/files/a75f0289..d29e49fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25828&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25828&range=01-02

  Stats: 17 lines in 1 file changed: 0 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/25828.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25828/head:pull/25828

PR: https://git.openjdk.org/jdk/pull/25828