RFR: 8356188: RISC-V: Cleanup effect of vmaskcmp_fp

[Dingli Zhang]

Hi all,
Please take a look and review this PR, thanks!

See "The RISC-V Instruction Set Manual" at https://riscv.org/technical/specifications/. In the Vector Floating-Point Compare Instructions section:

The destination mask vector register may be the same as the source vector mask register (v0).

Also, the integer form of `vmaskcmp` has no effect too, so remove the effect of vmaskcmp_fp.

### Testing
qemu-system 9.1.0 with UseRVV (ubuntu24.10):
* [x]  Run test/jdk/jdk/incubator/vector (fastdebug)

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Commit messages:
 - 8356188: RISC-V: Cleanup effect of vmaskcmp_fp

Changes: https://git.openjdk.org/jdk/pull/25055/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25055&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356188
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25055.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25055/head:pull/25055

PR: https://git.openjdk.org/jdk/pull/25055