RFR: 8356556: AArch64: No need for acquire fence in safepoint poll in FFM [v2]

[Anton Artemov]

> Hi, please consider the following changes:
> 
> On AArch64, the `acquire` bool argument of the `safepoint_poll()` method is removed, as the load-acquire `ldar` instruction in the `safepoint_poll()` implementation is not needed completely. It was used for observing the disarmed value when VMThread was used to disarm the Java threads, but currently JavaThreads disarm themselves. 
> 
> Tested in tiers 1 - 4.

Anton Artemov has updated the pull request incrementally with one additional commit since the last revision:

  8356556: Addressed reviewers' comments.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25829/files
  - new: https://git.openjdk.org/jdk/pull/25829/files/7a639980..6120a1e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25829&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25829&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25829.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25829/head:pull/25829

PR: https://git.openjdk.org/jdk/pull/25829