[lworld+fp16] RFR: 8341414: Add support for FP16 conversion routines [v3]

[Bhavana Kilambi]

> This patch adds intrinsic support for FP16 conversion routines to int/long/double and also the aarch64 backend support. This patch implements both scalar and vector versions for these conversions.
> 
> Performance numbers on aarch64 machine with SVE support :
> 
> 
> Benchmark                         (vectorDim)   Gain
> Float16OpsBenchmark.fp16ToDouble  1024          18.23
> Float16OpsBenchmark.fp16ToInt     1024          1.93
> Float16OpsBenchmark.fp16ToLong    1024          3.95
> 
> 
> The Gain column is the ratio between thrpt of this patch and the thrpt with the intrinsics disabled (which generates FP32 arithmetic).

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

  Address review comments

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1283/files
  - new: https://git.openjdk.org/valhalla/pull/1283/files/0809cedc..05b9347f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1283&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1283&range=01-02

  Stats: 31 lines in 3 files changed: 26 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/1283.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1283/head:pull/1283

PR: https://git.openjdk.org/valhalla/pull/1283