drm/xe/pf: Expose basic info about VFs in debugfs

We already have function to print summary about VFs, but we missed
to add debugfs attribute to make it visible. Do it now.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20250713103625.1964-6-michal.wajdeczko@intel.com