[riscv-port-jdk11u:riscv-port] RFR: 8294087: RISC-V: RVC: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops

[Gui Cao]

Hi,
Please help review this backport to riscv-port-jdk11u.
Backport of [JDK-8294087](https://bugs.openjdk.org/browse/JDK-8294087).
The original patch cannot be directly applied because of riscv-port-jdk11u do not have `emit_entry_barrier_stub ` C2CodeStub and no [JDK-8216557.](https://bugs.openjdk.org/browse/JDK-8216557.)

### Testing
- [x] Run tier1-tier3 tests on SOPHON SG2042 (fastdebug)

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Commit messages:
 - Backport 8294087: RISC-V: RVC: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/22/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=22&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294087
  Stats: 28 lines in 7 files changed: 26 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/22.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/22/head:pull/22

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/22