[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

[Dingli Zhang]

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:
- Tier1 passed without new failure on lp4a (release).

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

Commit messages:
 - 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/40/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=40&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/40.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/40/head:pull/40

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/40