RFR: 8340732: RISC-V: Refactor crc32 scalar version [v2]

[Hamlin Li]

> Hi,
> Can you help to review this patch?
> As discussed in https://github.com/openjdk/jdk/pull/20910#discussion_r1755150447, it's helpful to refactor the existing scalar version of crc32 intrinsic.
> Several refactoring are done in this pr,
> 1. Simplify the `len` usage, now it only decreases (i.e. change in one direction)
> 2. Simplify the code paths
> 3. Remove one instruction in `L_by4_loop`
> 4. Remove unnecessary code
> 5. Other misc
> 
> 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
 - bltz -> beqz
 - Initial commit

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Changes: https://git.openjdk.org/jdk/pull/21150/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21150&range=01
  Stats: 57 lines in 2 files changed: 9 ins; 26 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/21150.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21150/head:pull/21150

PR: https://git.openjdk.org/jdk/pull/21150