drm/xe: Add SVM init / close / fini to faulting VMs

Add SVM init / close / fini to faulting VMs. Minimual implementation
acting as a placeholder for follow on patches.

v2:
 - Add close function
v3:
 - Better commit message (Thomas)
 - Kernel doc (Thomas)
 - Update chunk array to be unsigned long (Thomas)
 - Use new drm_gpusvm.h header location (Thomas)
 - Newlines between functions in xe_svm.h (Thomas)
 - Call drm_gpusvm_driver_set_lock in init (Thomas)
v6:
 - Only compile if CONFIG_DRM_GPUSVM selected (CI, Lucas)
v7:
 - Only select CONFIG_DRM_GPUSVM if DEVICE_PRIVATE (CI)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-10-matthew.brost@intel.com