[riscv-port-jdk17u:riscv-port] RFR: 8295270: RISC-V: Clean up and refactoring for assembler functions [v2]

[Gui Cao]

> Please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8295270](https://bugs.openjdk.org/browse/JDK-8295270).
> [JDK-8295270](https://bugs.openjdk.org/browse/JDK-8295270) not clean，origin patch has no eden_allocate, which removed with [JDK-8290706](https://bugs.openjdk.org/browse/JDK-8290706)
> 
> Testing:
> 
> Tier1-3 passed without new failure on unmacthed (release).

Gui Cao has updated the pull request incrementally with one additional commit since the last revision:

  Add the missing IncompressibleRegion

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

Changes:
  - all: https://git.openjdk.org/riscv-port-jdk17u/pull/38/files
  - new: https://git.openjdk.org/riscv-port-jdk17u/pull/38/files/c3ee016b..09c99c42

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=38&range=01
 - incr: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=38&range=00-01

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/38.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/38/head:pull/38

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/38