[riscv-port-jdk17u:riscv-port] RFR: 8294087: RISC-V: RVC: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops

[Xiaolin Zheng]

May be not clean, for we do not have `C2CodeStub`.

Tested hotspot tier1~2 (fastdebug); other tiers are on the way.

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

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-jdk17u/pull/14/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=14&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294087
  Stats: 29 lines in 8 files changed: 25 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/14.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/14/head:pull/14

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/14