[riscv-port-jdk17u:riscv-port] RFR: 8305728: RISC-V: Use bexti instruction to do single-bit testing

[Dingli Zhang]

Hi, please review this backport to riscv-port-jdk17u.
Backport of [JDK-8305728](https://bugs.openjdk.org/browse/JDK-8305728). The original patch cannot be directly applied because jdk17u has no [JDK-8299089](https://bugs.openjdk.org/browse/JDK-8299089) and [JDK-8301995](https://bugs.openjdk.org/browse/JDK-8301995).

Testing:
- tier1-3 tests on QEMU-System w/ and w/o UseZbs (release build)
- tier1-3 tests on unmatched board w/o UseZbs (release build)

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Commit messages:
 - 8305728: RISC-V: Use bexti instruction to do single-bit testing

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/65/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=65&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305728
  Stats: 84 lines in 15 files changed: 12 ins; 0 del; 72 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/65.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/65/head:pull/65

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/65