drm/xe: account for dontneed in fdinfo purgeable

drm/xe: account for dontneed in fdinfo purgeable

Now that Xe supports explicit madvise WILLNEED/DONTNEED states,
userspace can mark memory in any placement as eligible for purging.
Update bo_meminfo to also include any BO explicitly marked as DONTNEED
in the purgeable statistics, ensuring fdinfo accurately reflects all
memory offered up for reclamation.

v2 (Sashiko):
  - Also update the drm_print_memory_stats() so we don't mask out !=
    SYSTEM

Assisted-by: Copilot:gemini-3.1-pro-preview
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Arvind Yadav <arvind.yadav@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260625152054.450125-7-matthew.auld@intel.com