RFR: 8365911: AArch64: Fix encoding error in sve_cpy for negative floats [v2]

[erifan]

On Wed, 3 Sep 2025 08:28:30 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> This may not be the case, `imm8 >> 8` doesn't equal to `imm8 & 0xff`
>
> What is the range of values you're trying to test?

It's hard to say, because it is actually the value bits of a fp8.

Simply put, the lower 8 bits are valid values. The remaining bits must be 0.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26951#discussion_r2318210500