tools/testing/cxl: Add a single-port host-bridge regression config

Jonathan reports that region creation fails when a single-port
host-bridge connects to a multi-port switch. Mock up that configuration
so a fix can be tested and regression tested going forward.

Reported-by: Bobo WL <lmw.bobo@gmail.com>
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: http://lore.kernel.org/r/20221010172057.00001559@huawei.com
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/166752184838.947915.2167957540894293891.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>