[riscv-port-jdk17u:riscv-port] RFR: 8301852: RISC-V: Optimize class atomic when order is memory_order_relaxed

[Dingli Zhang]

Hi, please review this backport to riscv-port-jdk17u.
Backport of [JDK-8301852](https://bugs.openjdk.org/browse/JDK-8301852). Applies cleanly.

Testing:
- Tier1-3 passed without new failure on unmacthed (release).

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Commit messages:
 - 8301852: RISC-V: Optimize class atomic when order is memory_order_relaxed

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/60/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=60&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301852
  Stats: 36 lines in 1 file changed: 18 ins; 1 del; 17 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/60.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/60/head:pull/60

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/60