RFR: 8356924: RISC-V: Clean up cost for vector instructions [v2]

[Dingli Zhang]

> As mentioned in https://bugs.openjdk.org/browse/JDK-8285790 regarding the ARM64 vector instruct modifications:
> Since the new rules are unique and setting different "ins_cost" makes no sense, we have switched to using the default cost.
> 
> Currently, there is a similar situation on RISC-V. Over half of the instructions in riscv_v.ad do not include ins_cost definitions. Additionally, as RVV nodes are also unique, we can unify the format by removing these ins_cost entries from riscv_v.ad.
> 
> ### Testing
> qemu-system 9.2.3 with UseRVV (ubuntu24.10):
> * [x]  Run test/jdk/jdk/incubator/vector (fastdebug)
> * [x]  Run test/hotspot/jtreg/compiler/vectorapi (fastdebug)

Dingli Zhang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Remove added ins_cost(VEC_COST) due to merging the main branch
 - Merge branch 'master' into master-remove-ins_cost
 - 8356924: RISC-V: Clean up cost for vector instructions

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25221/files
  - new: https://git.openjdk.org/jdk/pull/25221/files/80ab16a5..44521d8a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25221&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25221&range=00-01

  Stats: 23889 lines in 747 files changed: 8828 ins; 11491 del; 3570 mod
  Patch: https://git.openjdk.org/jdk/pull/25221.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25221/head:pull/25221

PR: https://git.openjdk.org/jdk/pull/25221