[jdk25u] RFR: 8368732: RISC-V: Detect support for misaligned vector access via hwprobe

[Dingli Zhang]

Hi,
Please help review this backport to jdk25u, thanks!

Backport of [JDK-8368732](https://bugs.openjdk.org/browse/JDK-8368732).

The original patch cannot be directly applied because of jdk25u do not have [JDK-8367253](https://bugs.openjdk.org/browse/JDK-8367253) or [JDK-8367103](https://bugs.openjdk.org/browse/JDK-8367103).

Manually checked the result on platforms w/wo fast misaligned vector accesses by running:

$ java -XX:+PrintFlagsFinal -version | grep AlignVector

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

Commit messages:
 - 8368732: RISC-V: Detect support for misaligned vector access via hwprobe

Changes: https://git.openjdk.org/jdk25u/pull/252/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=252&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368732
  Stats: 61 lines in 4 files changed: 47 ins; 1 del; 13 mod
  Patch: https://git.openjdk.org/jdk25u/pull/252.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/252/head:pull/252

PR: https://git.openjdk.org/jdk25u/pull/252