RFR: 8351159: Remaining cleanups in cpu/x86 after 32-bit x86 removal [v3]

[Anton Seoane Ampudia]

> This PR carries out cleanup on the `cpu` and `os_cpu` directories after the removal of the 32-bit x86 architecture from HotSpot.
> 
> Mainly, code guarded by `IA32` or `X32`, or `!AMD64` or `!LP64` in a x86 context, has been removed. These guards are now redundant (e.g. checking for 64bit on a x86 context) or the code blocks never executed (e.g. code under `#ifdef X32`). Additionally, x86 AD files have been merged.
> 
> Please note that this changeset limits itself to changes under `cpu/x86` and `os_cpu/x86`. Other cleanups are filed under a different RFE, and consequently addressed in a different PR: [JDK-8351149](https://github.com/openjdk/jdk/pull/27990).
> 
> **Testing:** passes tiers 1-5

Anton Seoane Ampudia has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 15 commits:

 - Merge changes from JDK-8369346
 - Apply review comments
 - Update copyright years
 - Reintroduce changes from JDK-8369569
 - Merge upstream changes
 - Merge x86 AD files
 - Roll back changes that are targeted in JDK-8354853
 - Cleanup _M_AMD64 from cpu/ and os_cpu/
 - Cleanup LP64_ONLY and NOT_LP64 from cpu/ and os_cpu/
 - Cleanup LP64 from os_cpu/
 - ... and 5 more: https://git.openjdk.org/jdk/compare/2c07214d...4e58e509

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Changes: https://git.openjdk.org/jdk/pull/27987/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27987&range=02
  Stats: 32669 lines in 32 files changed: 15343 ins; 16316 del; 1010 mod
  Patch: https://git.openjdk.org/jdk/pull/27987.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27987/head:pull/27987

PR: https://git.openjdk.org/jdk/pull/27987