RFR: 8345351: RISC-V: Rename macro-assembler routine cmpxchg_weak to weak_cmpxchg

[Fei Yang]

Hi, Please consider this trivial change.

We have macro-assembler routine names like `cmpxchg_narrow_value` and `weak_cmpxchg_narrow_value`.
We should rename `MacroAssembler::cmpxchg_weak` to `MacroAssembler::weak_cmpxchg` for consistency
in naming. This will also be consistent with names like `weakCompareAndSwapI`, `weakCompareAndSwapL` in AD files.

- [x] hotspot:tier1 test on linux-riscv64 platform.

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Commit messages:
 - 8345351: RISC-V: Rename macro-assembler routine cmpxchg_weak to weak_cmpxchg

Changes: https://git.openjdk.org/jdk/pull/22505/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22505&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345351
  Stats: 23 lines in 4 files changed: 0 ins; 0 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/22505.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22505/head:pull/22505

PR: https://git.openjdk.org/jdk/pull/22505