RFR: 8346478: RISC-V: Refactor add/sub assembler routines

[Fei Yang]

Hi, please consider this cleanup change.

Currently, we have mixed use of `addi` and `add(int64_t)`/`sub(int64_t)`. The former adds a 12-bit immediate while the latter
does not have a constraint on the immediate range. We should use `addi` when possible, which would help save one runtime check
about the immediate range and save the tmp register used by the latter as well. In order to make the code more readable, this
also introduces helper routines `subi`/`subiw` and adapts callsites of `addi`/`addiw` with negative immediates.

Testing: tier1-3 and gtest:all are clean on Premier-P550 SBC running Ubuntu-24.04.

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Commit messages:
 - 8346478: RISC-V: Refactor add/sub assembler routines

Changes: https://git.openjdk.org/jdk/pull/22804/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22804&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346478
  Stats: 392 lines in 19 files changed: 14 ins; 6 del; 372 mod
  Patch: https://git.openjdk.org/jdk/pull/22804.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22804/head:pull/22804

PR: https://git.openjdk.org/jdk/pull/22804