RFR: 8346478: RISC-V: Refactor add/sub assembler routines [v3]

[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.

Fei Yang has updated the pull request incrementally with one additional commit since the last revision:

  Revert unnecessary changes

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/22804/files
  - new: https://git.openjdk.org/jdk/pull/22804/files/58e9a0eb..4f8a6662

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22804&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22804&range=01-02

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 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