[jdk21u-dev] RFR: 8320397: RISC-V: Avoid passing t0 as temp register to MacroAssembler:: cmpxchg_obj_header/cmpxchgptr

[Gui Cao]

Hi, The same issue also exists in the jdk21u. I would like to backport this to jdk21u-dev. This is a risc-v specific change. Backport is clean, risk is low.

### Testing
- [ ] Run tier1-3 tests on SOPHON SG2042 (release)

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Commit messages:
 - Backport 0be0775a762edbefacf4188b4787b039153fe670

Changes: https://git.openjdk.org/jdk21u-dev/pull/1053/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1053&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320397
  Stats: 78 lines in 5 files changed: 4 ins; 4 del; 70 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1053.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1053/head:pull/1053

PR: https://git.openjdk.org/jdk21u-dev/pull/1053