[lworld] RFR: 8374887: [lworld] Cleanup around vgetfield/vputfield for x86

[Joel Sikström]

Hello,

This is a follow up from [JDK-8374093](https://bugs.openjdk.org/browse/JDK-8374093) cleaning up the x86 implementation as well.

Testing:
* hotspot_valhalla and jdk_valhalla on x86-64

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Commit messages:
 - 8374887: [lworld] Cleanup around vgetfield/vputfield for x86

Changes: https://git.openjdk.org/valhalla/pull/1875/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1875&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374887
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/1875.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1875/head:pull/1875

PR: https://git.openjdk.org/valhalla/pull/1875