drm/xe: Add SVM garbage collector

drm/xe: Add SVM garbage collector

Add basic SVM garbage collector which destroy a SVM range upon a MMU
UNMAP event. The garbage collector runs on worker or in GPU fault
handler and is required as locks in the path of reclaim are required and
cannot be taken the notifier.

v2:
 - Flush garbage collector in xe_svm_close
v3:
 - Better commit message (Thomas)
 - Kernel doc (Thomas)
 - Use list_first_entry_or_null for garbage collector loop (Thomas)
 - Don't add to garbage collector if VM is closed (Thomas)
v4:
 - Use %pe to print error (Thomas)
v5:
 - s/visable/visible (Thomas)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-16-matthew.brost@intel.com