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 <[email protected]>
Reported-by: Jonathan Cameron <[email protected]>
Link: http://lore.kernel.org/r/[email protected]
Reviewed-by: Vishal Verma <[email protected]>
Link: https://lore.kernel.org/r/166752184838.947915.2167957540894293891.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <[email protected]>

Author: djbw