[vectorIntrinsics+fp16] RFR: 8305563: [vectorapi]: Initial aarch64 backend implementation for FP16 operations [v2]

[Bhavana Kilambi]

> This patch adds aarch64 (Neon and SVE) backend implementation for the following FP16 operations for which C2 support was added in the commit https://github.com/openjdk/panama-vector/commit/7460d9327aac7d1d2ba6aed4e7137a417dbf6a97 -
> 
> Unary operations : AbsVHF, NegVHF
> Binary operations : AddVHF, SubVHF, MulVHF, DivVHF
> Ternary operations : AddReductionVHF, FmaVHF
> Conversion operations : VectorCastHF2D, VectorCastD2HF
> 
> Some of these operations on Neon machines, require features "fphp" and "asimdhp" to be available. Feature detection for these features have also been added.

Bhavana Kilambi has updated the pull request incrementally with one additional commit since the last revision:

  Addressed review comments

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

Changes:
  - all: https://git.openjdk.org/panama-vector/pull/217/files
  - new: https://git.openjdk.org/panama-vector/pull/217/files/64a7becc..12148848

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-vector&pr=217&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-vector&pr=217&range=00-01

  Stats: 31 lines in 4 files changed: 17 ins; 6 del; 8 mod
  Patch: https://git.openjdk.org/panama-vector/pull/217.diff
  Fetch: git fetch https://git.openjdk.org/panama-vector.git pull/217/head:pull/217

PR: https://git.openjdk.org/panama-vector/pull/217