RFR: 8367103: RISC-V: store cpu features in a bitmap

[Hamlin Li]

Hi,
Can you help to review this patch?

Currently, the cpu features of riscv are stored in separate RVFeature subclasses.
But to support the store/restore CPU features for aot in the future, we need to store the cpu features in a continuous memory.
As the riscv extensions are introduced continuously, I think it's better to do it via an simple bitmap at the beginning.
Currently, just suppose the non-extension features will not be stored in aot image, so I also split the extension and non-extenion features. When we implement the related aot feature in the short future, we can revisit the way of splitting the features. Currently, just change the storage way of cpu features, lay the foundation for future aot.

Thanks

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Commit messages:
 - refine
 - split extension and non-extension features
 - remove RVFeatureValue::_enabled
 - rename own to current
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/27152/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27152&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367103
  Stats: 214 lines in 2 files changed: 144 ins; 4 del; 66 mod
  Patch: https://git.openjdk.org/jdk/pull/27152.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27152/head:pull/27152

PR: https://git.openjdk.org/jdk/pull/27152