RFR: 8327794: RISC-V: enable extension features based on impid

[Hamlin Li]

Hi,
Can you review the patch? it enables extension features based on impid.
Thanks!

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/18191/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18191&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327794
  Stats: 6 lines in 1 file changed: 4 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18191.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18191/head:pull/18191

PR: https://git.openjdk.org/jdk/pull/18191