drm/xe/configfs: Use tree-like output in documentation

When documenting the directories, use an output similar to the `tree`
command and add VFs and missing attributes.

Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Link: https://lore.kernel.org/r/20250821-psmi-v5-9-34ab7550d3d8@intel.com


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