RFR: 8367048: RISC-V: Correct pipeline descriptions of the architecture

[Hamlin Li]

On Mon, 8 Sep 2025 05:13:32 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi,
> Can you help to review this patch? Thanks!
> 
> This patch updates the RISC-V pipeline attributes to variable_size_instructions to properly account for the 2-byte compressed instructions from the C extension. 
> Furthermore, it increases the max_instructions_per_bundle to 4 and adjusts the instruction_unit_size to match 4-issue RISC-V hardware like the UR-CP100.
> 
> ### Test
> - [x] Run tier1 and tier2 on sg2042

Marked as reviewed by mli (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27134#pullrequestreview-3196372198