linuxkpi: Add default_groups field to struct kobj_type

We don't use it, but it is set by the DRM drivers.

Reviewed by:	manu
Approved by:	manu
Differential Revision:	https://reviews.freebsd.org/D39051

sys/compat/linuxkpi/common/include/linux/kobject.h

@@ -47,6 +47,7 @@ struct kobj_type {
 	void (*release)(struct kobject *kobj);
 	const struct sysfs_ops *sysfs_ops;
 	struct attribute **default_attrs;
+	const struct attribute_group **default_groups;
 };
 
 extern const struct kobj_type linux_kfree_type;