[jdk21u] RFR: 8318953: RISC-V: Small refactoring for MacroAssembler::test_bit

[Gui Cao]

Hi, this backport to make the test_bit assember function more simpler and to improve performance when the parameter (1UL << bit_pos) exceeds 32-bit range. This is a risc-v specific change. Backport is clean, risk is low.
### Testing:
qemu 8.1.50:
- [x] Tier1 tests (release)

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Commit messages:
 - Backport 988e1dfe6ec9b5e77d2e8a78eb792a127c6fe907

Changes: https://git.openjdk.org/jdk21u/pull/301/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=301&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318953
  Stats: 10 lines in 3 files changed: 6 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u/pull/301.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/301/head:pull/301

PR: https://git.openjdk.org/jdk21u/pull/301