RFR: 8351151: Clean up x86 template interpreter after 32-bit x86 removal

[Aleksey Shipilev]

x86 template interpreter carries `_LP64`-predicated code blocks that were supporting 32-bit x86. With that port gone, we can clean up the x86 template interpreter. I have checked no superfluous `LP64`, `AMD64`, `IA32` defines are left in affected files.

Where obvious, I inlined `r15_thread` and `c_arg*`. Left the uses that assign these args to symbolic locals that have meaningful names.

`verify_FPU` is also no-op now, removed that. There are related cleanups in compilers and runtime we need to do first, before we fully remove `VerifyFPU` flag. This change fans out a little to other platform template interpreters to remove `verify_FPU` as well.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `tier1`
 - [ ] Linux x86_64 server fastdebug, `all`

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Commit messages:
 - Revert one incorrect replacement
 - Touchups
 - Fix

Changes: https://git.openjdk.org/jdk/pull/24251/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24251&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351151
  Stats: 1165 lines in 15 files changed: 2 ins; 1040 del; 123 mod
  Patch: https://git.openjdk.org/jdk/pull/24251.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24251/head:pull/24251

PR: https://git.openjdk.org/jdk/pull/24251