RFR: 8367253: RISC-V: refactor dependent cpu extensions [v2]

[Hamlin Li]

> Hi,
> Can you help to review this patch?
> 
> Dependent extensions could be improved in several ways.
> 
> Currently, the dependent cpu extensions are processed in 2 separate places:
> 1. update_flag() when calling VM_Version::setup_cpu_available_features()
> 2. at the end of VM_Version::common_initialize().
> But we can do it in one single place, that is update_flag().
> 
> And, dependency relationship can only be expressed in (1:1) way, can not be expressed (1:N) way, but in fact some extensions can depend on several different other extensions, for example, zvfh depends on zvf and rvv. It's would be better to support this (1:N) relationship.
> 
> Thanks!

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

 - merge master
 - remove obsolete extension dependency code
 - initial commit

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Changes: https://git.openjdk.org/jdk/pull/27171/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27171&range=01
  Stats: 143 lines in 2 files changed: 52 ins; 30 del; 61 mod
  Patch: https://git.openjdk.org/jdk/pull/27171.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27171/head:pull/27171

PR: https://git.openjdk.org/jdk/pull/27171