RFR: 8368732: RISC-V: Detect support for misaligned vector access via hwprobe

[Fei Yang]

Hi, this is a followup change after [JDK-8368366](https://bugs.openjdk.org/browse/JDK-8368366).

According to the latest RISC-V linux hardware probing syscall [1], the performance of misaligned memory accesses has been divided into two cases: `RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF` and `RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF` for scalar and vector respectively. 

This aligns `AlignVector` with `RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF`. That is if the misaligned vector access is fast, we set `AlignVector` to false in the hope that it will save instructions handling address alignment thus improves performance.

This choose to keep the use of `RISCV_HWPROBE_KEY_CPUPERF_0` which is now deprecated and returns similar values
to `RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF` for backward compatibility with old linux kernels.

Manually checked the result on platforms w/wo fast misaligned vector accesses by running: 
`$java -XX:+PrintFlagsFinal -version | grep AlignVector`

[1] https://docs.kernel.org/arch/riscv/hwprobe.html

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Commit messages:
 - RISC-V: Detect support for misaligned vector access via hwprobe

Changes: https://git.openjdk.org/jdk/pull/27512/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27512&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368732
  Stats: 38 lines in 4 files changed: 28 ins; 1 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/27512.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27512/head:pull/27512

PR: https://git.openjdk.org/jdk/pull/27512