[riscv-port-jdk11u:riscv-port] RFR: 8293474: RISC-V: Unify the way of moving function pointer

[Dingli Zhang]

Please review this backport to riscv-port-jdk11u.
Backport of [JDK-8293474](https://bugs.openjdk.org/browse/JDK-8293474).
Applies not cleanly due to context difference, and changes in `shenandoahBarrierSetAssembler_riscv.cpp` have been modified previously.

Testing:
- Tier1 passed without new failure on lp4a (release).

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Commit messages:
 - 8293474: RISC-V: Unify the way of moving function pointer

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/33/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=33&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293474
  Stats: 16 lines in 2 files changed: 2 ins; 8 del; 6 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/33.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/33/head:pull/33

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/33