RFR: 8319781: RISC-V: Refactor UseRVV related checks [v4]

[Hamlin Li]

> Hi,
> Can you review the patch to refactor the code related UseRVV checks?
> Thanks!
> 
> There are some code (flag setting/checking) depending on UseRVV's value, these code should be refactored, especially after the change of https://bugs.openjdk.org/browse/JDK-8319408:
> 1. some code needs to get the final UseRVV's value rather than the initial value, e.g. ChaCha20 intrinsic.
> 2. refactored to be more readable.
> 3. also add note to make sure the future code get the final UseRVV value instead of inital value.

Hamlin Li has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - merge master
 - remove code setting SpecialEncodeISOArray
 - refine comments
 - Initial commit

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Changes: https://git.openjdk.org/jdk/pull/16580/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16580&range=03
  Stats: 53 lines in 2 files changed: 21 ins; 29 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16580.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16580/head:pull/16580

PR: https://git.openjdk.org/jdk/pull/16580