RFR: 8367048: RISC-V: Correct pipeline descriptions of the architecture [v2]

[Dingli Zhang]

> 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

Dingli Zhang has updated the pull request incrementally with one additional commit since the last revision:

  fix typo

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27134/files
  - new: https://git.openjdk.org/jdk/pull/27134/files/99846cd6..b5d87735

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27134&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27134&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27134.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27134/head:pull/27134

PR: https://git.openjdk.org/jdk/pull/27134