RFR: 8318827: RISC-V: Improve readability of fclass result testing [v2]

[Feilong Jiang]

> Hi, please consider.
> 
> Currently, we test results of `fclass` instruction with hard-coded bits which has bad readability. This patch adds an enumeration of the flcass mask bits for ease of use.
> 
> Testing:
> 
> - [ ] tier1 with release build

Feilong Jiang has updated the pull request incrementally with one additional commit since the last revision:

  adjust enum name style

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16362/files
  - new: https://git.openjdk.org/jdk/pull/16362/files/069bb876..593913ef

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16362&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16362&range=00-01

  Stats: 24 lines in 4 files changed: 0 ins; 0 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/16362.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16362/head:pull/16362

PR: https://git.openjdk.org/jdk/pull/16362