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.

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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Issue

• JDK-8342884: RISC-V: verify float <--> float16 conversion (Sub-task - P4)

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