drm/xe: Add drm_gpusvm_devmem to xe_bo

Add drm_gpusvm_devmem to xe_bo. Required to enable SVM migrations.

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/20250306012657.3505757-23-matthew.brost@intel.com