RFR: 8316654: remove edundant dmb after casal instruction

[Sun Jianye]

Hi,all.
The `casal` means a CAS operate with both load-acquire and store-release semantics.It looks like the subsequent dmb is redundant. Can we remove it?

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Commit messages:
 - remove dmb when using lse cas instructions

Changes: https://git.openjdk.org/jdk/pull/15856/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15856&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316654
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15856.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15856/head:pull/15856

PR: https://git.openjdk.org/jdk/pull/15856