nfit, libnvdimm: deprecate the generic SMART ioctl

The kernel's ND_IOCTL_SMART_THRESHOLD command is based on a payload
definition that has become broken / out-of-sync with recent versions of
the NVDIMM_FAMILY_INTEL definition. Deprecate the use of the
ND_IOCTL_SMART_THRESHOLD command in favor of the ND_CMD_CALL approach
taken by NVDIMM_FAMILY_{HPE,MSFT}, where we can manage the per-vendor
variance in userspace.

In a couple years, when the new scheme is widely deployed in userspace
packages, the ND_IOCTL_SMART_THRESHOLD support can be removed. For now
we prevent new binaries from compiling against the kernel header
definitions, but kernel still compatible with old binaries. The
libndctl.h [1] header is now the authoritative interface definition for
NVDIMM SMART.

[1]: https://github.com/pmem/ndctl


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