drm/xe/tests: Support CPU page-table updates in the migrate test

The migrate test currently supports only GPU pagetable updates and
will thus break if we fix the CPU pagetable update selection.

Fix the migrate test first.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>