[riscv-port-jdk17u:riscv-port] RFR: 8296916: RISC-V: Move some small macro-assembler functions to header file

[Dingli Zhang]

Please review this backport to riscv-port-jdk17u.
Backport of [JDK-8296916](https://bugs.openjdk.org/browse/JDK-8296916).
The original patch cannot be directly applied because jdk17u has no [JDK-8294100](https://bugs.openjdk.org/browse/JDK-8294100) with `MacroAssembler::object_move` and has no `vneg_v`, either.

Testing:

Tier1-3 passed without new failure on unmacthed (release).

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Commit messages:
 - 8296916: RISC-V: Move some small macro-assembler functions to header file

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/50/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=50&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296916
  Stats: 281 lines in 3 files changed: 101 ins; 140 del; 40 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/50.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/50/head:pull/50

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/50