RFR: 8357968: RISC-V: Interpreter volatile reference stores with G1 are not sequentially consistent

[Robbin Ehn]

Hi please consider.

As ref: https://github.com/openjdk/jdk/pull/25483
As suggested in that PR - I removed these helpers as it's very hard to see that you get registers clobbered.

Sanity tested, running t1.

/Robbin

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/25502/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25502&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357968
  Stats: 27 lines in 1 file changed: 0 ins; 18 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/25502.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25502/head:pull/25502

PR: https://git.openjdk.org/jdk/pull/25502