RFR: 8330735: RISC-V: No need to move sp to tmp register in set_last_Java_frame

[Feilong Jiang]

Hi, please review this refactoring to remove the unnecessary move from sp to temp register.

There is no restriction for riscv when using `sp` as an operand in instructions. So we do not have to move the sp register to a temp register before we store `last_java_sp`.

Testing:

- [x] Tier1-3 (linux-riscv64, release)

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Commit messages:
 - unnecessary mv from sp to tmp register

Changes: https://git.openjdk.org/jdk/pull/18875/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18875&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330735
  Stats: 12 lines in 3 files changed: 0 ins; 4 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/18875.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18875/head:pull/18875

PR: https://git.openjdk.org/jdk/pull/18875