drm/xe: Improve devcoredump documentation

Let the introduction be useful for both userspace and kernel. Also
improve the formatting to wire up later to the documentation build.

Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241102161254.1818604-2-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>