ndtest: Add compatability string to treat it as PAPR family

Since this module is written to be platform agnostic, the module is made
part of the PAPR_FAMILY. ndctl identifies the family using the compatible
string inside of_node dir-entry.

Signed-off-by: Santosh Sivaraj <santosh@fossix.org>
Link: https://lore.kernel.org/r/20201222042240.2983755-3-santosh@fossix.org


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