[lworld+fp16] RFR: 8330021: AArch64: Add backend support for FP16 add operation [v2]

[Bhavana Kilambi]

> This commit [1] adds initial support for FP16 operations and adds backend support for FP16 add operation for X86. This task adds backend support for scalar and vector FP16 add operation on aarch64.
> 
> [1] https://github.com/openjdk/valhalla/commit/f03fb4e4ee4d59ed692d0c26ddce260511f544e7#diff-a799ce8da7f3062bb3699beb65aae504840c649942032e325c2a50f88a2869ad

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

  Add a missing return statement in the ad file

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1096/files
  - new: https://git.openjdk.org/valhalla/pull/1096/files/1d09ba44..afdd81c6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1096&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1096&range=00-01

  Stats: 6 lines in 2 files changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/1096.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1096/head:pull/1096

PR: https://git.openjdk.org/valhalla/pull/1096