[lldb][FreeBSD] Fix NativeRegisterContextFreeBSD_{arm,mips64,powerpc} declarations...

[lldb][FreeBSD] Fix NativeRegisterContextFreeBSD_{arm,mips64,powerpc} declarations (#101403)

Similar to #97796, fix the type of the `native_thread` parameter for the
arm, mips64 and powerpc variants of `NativeRegisterContextFreeBSD_*`.

Otherwise, this leads to compile errors similar to:

```
lldb/source/Plugins/Process/FreeBSD/NativeRegisterContextFreeBSD_powerpc.cpp:85:39: error: out-of-line definition of 'NativeRegisterContextFreeBSD_powerpc' does not match any declaration in 'lldb_private::process_freebsd::NativeRegisterContextFreeBSD_powerpc'
   85 | NativeRegisterContextFreeBSD_powerpc::NativeRegisterContextFreeBSD_powerpc(
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

(cherry picked from commit 7088a5ed880f29129ec844c66068e8cb61ca98bf)