RFR: 8323748: RISC-V: Add Zfh probe code

[Hamlin Li]

Hi,
Can you review this simple patch to add zfh probe code which is a remaining task of [JDK-8318227](https://bugs.openjdk.org/browse/JDK-8318227)?
Thanks.

FYI: zfh extension is in the [kernel code](https://github.com/torvalds/linux/blob/master/arch/riscv/include/uapi/asm/hwprobe.h) already.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/17498/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17498&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323748
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17498.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17498/head:pull/17498

PR: https://git.openjdk.org/jdk/pull/17498