RFR: 8368724: RISC-V: Check if unaligned_access is enabled before use [v3]

[Anjian Wen]

> we can notice that the `unaligned_access.value()` can only be used when the `unaligned_access.enabled()` is true, so we add the check here before use
> 
> Manually checked the result on platforms w/wo fast misaligned accesses by running: $java -XX:+PrintFlagsFinal -version | grep AvoidUnalignedAccess

Anjian Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into add_unaligned_access_check
 - delete AvoidUnalignedAccesses and extra unnecessary check
 - RISC-V: Add unaligned access check

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Changes: https://git.openjdk.org/jdk/pull/27510/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27510&range=02
  Stats: 34 lines in 5 files changed: 0 ins; 6 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/27510.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27510/head:pull/27510

PR: https://git.openjdk.org/jdk/pull/27510