libnvdimm, e820: skip module loading when no type-12

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: Andy Lutomirski <luto@amacapital.net>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>