drm/xe/pt: unify xe_pt_svm_pre_commit with userptr

drm/xe/pt: unify xe_pt_svm_pre_commit with userptr

We now use the same notifier lock for SVM and userptr, with that we can
combine xe_pt_userptr_pre_commit and xe_pt_svm_pre_commit.

v2: (Matt B)
  - Re-use xe_svm_notifier_lock/unlock for userptr.
  - Combine svm/userptr handling further down into op_check_svm_userptr.
v3:
  - Only hide the ops if we lack DRM_GPUSVM, since we also need them for
    userptr.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250828142430.615826-18-matthew.auld@intel.com