drm/xe: Use proper vram offset

In xe_migrate functions, use proper vram io offset of the
tiles while calculating addresses.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>