[riscv-port-jdk17u:riscv-port] RFR: 8291893: riscv: remove fence.i used in user space [v3]

[Dingli Zhang]

> Please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8291893](https://bugs.openjdk.org/browse/JDK-8291893).
> 
> The original patch cannot be directly applied because of the line number, but there are no other additional changes.
> 
> Testing:
> - Tier1 passed without new failure on unmacthed (release).

Dingli Zhang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'riscv-port' into backport-JDK-8291893
 - rebase
 - 8291893: riscv: remove fence.i used in user space

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

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/13/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=13&range=02
  Stats: 77 lines in 10 files changed: 8 ins; 63 del; 6 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/13.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/13/head:pull/13

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/13