RFR: 8342884: RISC-V: verify float <--> float16 conversion

[Hamlin Li]

Hi,
Can you help to review this simple patch? it removes the `Experimental` of the `UseZvfh`.
Thanks

Currently, only float <--> float16 conversions use Zvfh extension, I've run the jmh tests on bananapi, the performance result shows it's good.
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Benchmark-XX:+UseZfh -XX:+UnlockExperimentalVMOptions -XX:+/-UseZvfh | (size) | Mode | Cnt | Score -intrinsic | Score +intrinsic | Error | Units | Improvement
-- | -- | -- | -- | -- | -- | -- | -- | --
Fp16ConversionBenchmark.float16ToFloat | 2048 | avgt | 10 | 8129.72 | 4729.125 | 71.937 | ns/op | 1.719
Fp16ConversionBenchmark.float16ToFloatMemory | 2048 | avgt | 10 | 16.9 | 16.894 | 0.002 | ns/op | 1
Fp16ConversionBenchmark.floatToFloat16 | 2048 | avgt | 10 | 12561.962 | 3767.944 | 12.652 | ns/op | 3.334
Fp16ConversionBenchmark.floatToFloat16Memory | 2048 | avgt | 10 | 18.146 | 18.147 | 0.003 | ns/op | 1

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Commit messages:
 - initial commit
 - Merge branch 'openjdk:master' into master
 - Revert "initial commit"
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/21664/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21664&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342884
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21664.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21664/head:pull/21664

PR: https://git.openjdk.org/jdk/pull/21664