If there are no persistent memory ranges present then don't bother
creating the platform device.  Otherwise, it loads the full libnvdimm
sub-system only to discover no resources present.
Reported-by: NAndy Lutomirski <luto@amacapital.net>
Acked-by: NAndy Lutomirski <luto@amacapital.net>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>