drm/xe/vm: Add an identifier in xe_vma_ops for svm prefetch

drm/xe/vm: Add an identifier in xe_vma_ops for svm prefetch

Add a flag in xe_vma_ops to determine whether it has svm prefetch ops or
not.

v2:
 - s/false/0 (Matthew Brost)

v3:
 - s/XE_VMA_OPS_HAS_SVM_PREFETCH/XE_VMA_OPS_FLAG_HAS_SVM_PREFETCH

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://lore.kernel.org/r/20250513040228.470682-8-himal.prasad.ghimiray@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>