dax: Create a dax device_type

Move the open coded release method and attribute groups to a 'struct
device_type' instance.

Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Reviewed-by: NAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Link: https://lore.kernel.org/r/157309904365.1582359.5451327195246651379.stgit@dwillia2-desk3.amr.corp.intel.com

drivers/dax/bus.c

@@ -373,6 +373,11 @@ static void dev_dax_release(struct device *dev)
 	kfree(dev_dax);
 }
 
+static const struct device_type dev_dax_type = {
+	.release = dev_dax_release,
+	.groups = dax_attribute_groups,
+};
+
 static void unregister_dev_dax(void *dev)
 {
 	struct dev_dax *dev_dax = to_dev_dax(dev);
@@ -430,8 +435,7 @@ struct dev_dax *__devm_create_dev_dax(struct dax_region *dax_region, int id,
 	else
 		dev->class = dax_class;
 	dev->parent = parent;
-	dev->groups = dax_attribute_groups;
-	dev->release = dev_dax_release;
+	dev->type = &dev_dax_type;
 	dev_set_name(dev, "dax%d.%d", dax_region->id, id);
 
 	rc = device_add(dev);