x86: Harmonize GENERIC and MINIMAL

[des]

Summary

• Reorder MINIMAL so everything is in the same order as in GENERIC.

• Wherever comments diverged, except for the explanatory comment at the top, copy the GENERIC version to MINIMAL.

• Add KDTRACE_FRAME to i386 GENERIC; it was already in MINIMAL, and adding it to GENERIC seemed like the more correct move.

With these changes, MINIMAL is a strict subset of GENERIC, apart from
the identifier and the explanatory comment at the top.

[imp]

Thanks for doing this!