[jdk21u-dev] RFR: 8315652: RISC-V: Features string uses wrong separator for jtreg

[Gui Cao]

Hi, I would like to backport https://bugs.openjdk.org/browse/JDK-8315652 to jdk21-dev. With this backport, features string looks more reasonable and it will be easier to match specific extensions e.g. vector. It will also be easier to backport jdk mainline test cases to jdk21u-dev in the future. RISC-V specific change, risk is low.

### Testing
- [x]  Run tier1 tests on SOPHON SG2042 (release)

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

Commit messages:
 - Backport 8315652: RISC-V: Features string uses wrong separator for jtreg

Changes: https://git.openjdk.org/jdk21u-dev/pull/472/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=472&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315652
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/472.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/472/head:pull/472

PR: https://git.openjdk.org/jdk21u-dev/pull/472