RFR: 8374525: RISC-V: Several masked float16 vector operations are not supported

[Dingli Zhang]

Hi,
Can you help to review this patch? Thanks!

Currently, the masked versions of the following 8 Float16 operations are not supported.
But we return true in `Matcher::match_rule_supported_vector_masked` for these operations
on RISC-V platforms with Zvfh. We need to explicitly disable them on this CPU platform
to make it clear.

 Op_AddVHF:
 Op_SubVHF:
 Op_MulVHF:
 Op_DivVHF:
 Op_MaxVHF:
 Op_MinVHF:
 Op_SqrtVHF:
 Op_FmaVHF:

When the support for Float16 vector classes is added in VectorAPI and the masked
Float16 IR can be generated, these masked operations will be enabled and relevant
backend support added.

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Commit messages:
 - 8374525: RISC-V: Several masked float16 vector operations are not supported

Changes: https://git.openjdk.org/jdk/pull/29035/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29035&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374525
  Stats: 19 lines in 1 file changed: 17 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29035.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29035/head:pull/29035

PR: https://git.openjdk.org/jdk/pull/29035