EDAC, skx: Fix skx_edac build error when ACPI_NFIT=m

Prevent build error when CONFIG_ACPI_NFIT=m and CONFIG_EDAC_SKX=y by
limiting EDAC_SKX based on how ACPI_NFIT is set.

Fixes this build error:
  drivers/edac/skx_edac.o: In function `get_nvdimm_info':
  ../drivers/edac/skx_edac.c:399: undefined reference to `nfit_get_smbios_id'

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Fixes: 58ca9ac1 ("EDAC, skx_edac: Detect non-volatile DIMMs")
Link: http://lkml.kernel.org/r/3af91354-8e19-d2af-1bba-ced8dce053f1@infradead.org


Signed-off-by: Borislav Petkov <bp@suse.de>