RFR: 8294087: RISC-V: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops [v2]

[Xiaolin Zheng]

> This is a trivial refactoring for some instruction alignment assertions. Due to the fact that the `assert (__ offset() % 4 == 0)` is getting used more, this small patch is extracted first to simplify code reviewing.
> This patch doesn't change the code behavior.
> Tested hotspot tier1 and tier2 together with other patches on QEMU.

Xiaolin Zheng has updated the pull request incrementally with two additional commits since the last revision:

 - Modifications as to review comments
 - RISC-V: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10370/files
  - new: https://git.openjdk.org/jdk/pull/10370/files/16d601ba..88256ff1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10370&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10370&range=00-01

  Stats: 25 lines in 6 files changed: 18 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/10370.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10370/head:pull/10370

PR: https://git.openjdk.org/jdk/pull/10370