RFR: 8368724: RISC-V: Check if unaligned_access is enabled before use [v4]

[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 incrementally with one additional commit since the last revision:

  delete whitespace

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27510/files
  - new: https://git.openjdk.org/jdk/pull/27510/files/910840da..c1b209fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27510&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27510&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 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