x86/configs: Add x86 debugging Kconfig fragment plus docs

The kernel has a wide variety of debugging options to help catch
and squash bugs.  However, new debugging is added all the time and
the existing options can be hard to find.

Add a Kconfig fragment with the debugging options which tip
maintainers expect to be used to test contributions.

This should make it easier for contributors to test their code and
find issues before submission.

  [ bp: Add to "make help" output, fix DEBUG_INFO selection as pointed
        out by Nathan Chancellor <nathan@kernel.org>. ]

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220331175728.299103A0@davehans-spike.ostc.intel.com