RFR: 8369979: Flag UsePopCountInstruction was accidentally disabled on PPC64

[David Briemann]

Reenables the flag UsePopCountInstruction for PPC in `src/hotspot/cpu/ppc/vm_version_ppc.cpp` to reactivate the support for popcount intrinsics on PPC.

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Commit messages:
 - 8369979: Flag UsePopCountInstruction was accidentally disabled on PPC64

Changes: https://git.openjdk.org/jdk/pull/27843/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27843&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369979
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27843.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27843/head:pull/27843

PR: https://git.openjdk.org/jdk/pull/27843