tools/testing/cxl: Mock dvsec_ranges()

For test purposes, pretend that that CXL DVSEC ranges are not in active
use and the device is ready CXL.mem operation.

Link: https://lore.kernel.org/r/164298431119.3018233.17175518196764977542.stgit@dwillia2-desk3.amr.corp.intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>