drm/xe/tests/xe_migrate.c: Add vram to vram KUNIT test

Add missing kunit test to migrate a bo from vram to vram

Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: "Michael J. Ruhl" <michael.j.ruhl@intel.com>
Signed-off-by: David Kershner <david.kershner@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>