cxl/acpi: Autoload driver for 'cxl_acpi' test devices

In support of CXL unit tests in the ndctl project, arrange for the
cxl_acpi driver to load in response to the registration of cxl_test
devices.

Reported-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/165853775783.2430596.13637998086505316619.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>