Revert "libnvdimm, of_pmem: workaround OF_NUMA=n build error"

With commit df3f1264 ("libnvdimm, of_pmem: use dev_to_node() instead
of of_node_to_nid()") it is now possible to allow of_pmem to be built as
a module as originally implemented.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/Kconfig

@@ -103,8 +103,7 @@ config NVDIMM_DAX
 	  Select Y if unsure
 
 config OF_PMEM
-	# FIXME: make tristate once OF_NUMA dependency removed
-	bool "Device-tree support for persistent memory regions"
+	tristate "Device-tree support for persistent memory regions"
 	depends on OF
 	default LIBNVDIMM
 	help