libnvdimm, nfit: report multiple interface codes per-dimm

Starting with ACPI 6.1 an NFIT table will report multiple 'NVDIMM
Control Region Structure' instances per-dimm, one for each supported
format interface.  Report that code in the following format in sysfs:

    nmemX/nfit/formats
    nmemX/nfit/format
    nmemX/nfit/format1
    nmemX/nfit/format2
    ...
    nmemX/nfit/formatN

Where format2 - formatN are theoretical as there are no known DIMMs with
support for more than two interface formats.

This layout is compatible with existing libndctl binaries that only
expect one code per-dimm as they will ignore nmemX/nfit/formats and
nmemX/nfit/formatN.

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