RFR: 8290324: Move atomic operations outside of os_xxx.hpp [v2]

[Ioi Lam]

> The os_xxx.hpp files inject extra methods/fields that are specific to atomic operations into the `os` class. However, the injected methods/fields are used only by a specific os/cpu combination. Therefore, they should not be inside the `os` class, which should contain only APIs that are used across platforms.
> 
> - For ports where the `atomic_copy64()` function is used in a single file, I moved it as an inline function in that file
> - Otherwise it's moved to `atomic_<os>_<cpu>.hpp`
> - The linux/arm port is a little more involved, but the new code should be a little cleaner than the old code.

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into 8290324-move-atomic-ops-outside-os-hpp
 - 8290324: Move atomic operations outside of os_xxx.hpp

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9501/files
  - new: https://git.openjdk.org/jdk/pull/9501/files/e8402000..2ba6addb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9501&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9501&range=00-01

  Stats: 1641 lines in 47 files changed: 1416 ins; 172 del; 53 mod
  Patch: https://git.openjdk.org/jdk/pull/9501.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9501/head:pull/9501

PR: https://git.openjdk.org/jdk/pull/9501