[riscv-port-jdk17u:riscv-port] RFR: 8291947: riscv: fail to build after JDK-8290840

[Gui Cao]

Please review this backport to riscv-port-jdk17u.
Backport of [JDK-8291947](https://bugs.openjdk.org/browse/JDK-8291947). 
In the current version, https://bugs.openjdk.org/browse/JDK-8290840 has not been refactored, so the issues corresponding to the original issue do not exist. compared to the original patch, the icache_flush function is removed in a different location.

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

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Commit messages:
 - 8291947: riscv: fail to build after JDK-8290840

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/15/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=15&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291947
  Stats: 20 lines in 2 files changed: 0 ins; 19 del; 1 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/15.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/15/head:pull/15

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/15