RFR: 8321001: RISC-V: C2 SignumVF

[Hamlin Li]

Hi,
Can you review the patch to add intrinisc SignumVF/SignumVD on riscv?
Thanks

## Test
test/hotspot/jtreg/compiler/intrinsics/
and tests found:
grep -nr test/hotspot/jtreg/ -we Math.signum
and test found:
grep -nr test/jdk/ -we Math.signum

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16925/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16925&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321001
  Stats: 39 lines in 4 files changed: 39 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16925.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16925/head:pull/16925

PR: https://git.openjdk.org/jdk/pull/16925