[lworld+fp16] RFR: 8336406: Add support for FP16 binary operations

[Bhavana Kilambi]

This patch adds middle end support in C2 for a few FP16 binary operations, namely - subtract, multiply, divide, min and max. It also adds aarch64 backend support for these operations.

Tested JTREG tests -
hotspot/jtreg/compiler/vectorization/TestFloat16VectorOps.java, hotspot/jtreg/compiler/vectorization/TestFloat16VectorReinterpretConv.java, hotspot/jtreg/compiler/intrinsics/float16 and test/jdk/java/lang/Float16 and they successfully pass on aarch64 and x86 machines.

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

Commit messages:
 - 8336406: Add support for FP16 binary operations

Changes: https://git.openjdk.org/valhalla/pull/1175/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1175&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336406
  Stats: 1146 lines in 27 files changed: 870 ins; 175 del; 101 mod
  Patch: https://git.openjdk.org/valhalla/pull/1175.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1175/head:pull/1175

PR: https://git.openjdk.org/valhalla/pull/1175