RFR: 8367611: Enable vblendvp[sd] on Future ECore [v2]

[Mohamed Issa]

> The upcoming ECore platforms will benefit from using `vblendvps` and `vblendvpd` instructions when the destination register is the same as the source register. This change takes that situation into account.
> 
> The JTREG test shown below was used to verify correctness against the [OpenJDK v26-b15](https://github.com/openjdk/jdk/releases/tag/jdk-26%2B15) baseline build.
> 
> 1. `jtreg:test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java`

Mohamed Issa has updated the pull request incrementally with one additional commit since the last revision:

  Use function to identify Darkmont cores instead of global flag

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27354/files
  - new: https://git.openjdk.org/jdk/pull/27354/files/078a295d..88ac7733

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27354&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27354&range=00-01

  Stats: 18 lines in 4 files changed: 6 ins; 10 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/27354.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27354/head:pull/27354

PR: https://git.openjdk.org/jdk/pull/27354