drm: Implement dummies for debugfs helpers

In case where debugfs support is disabled, define dummy functions to
avoid the need for #ifdefery in drivers.

Based on an earlier patch by Arnd Bergmann.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drmP.h

@@ -1478,6 +1478,30 @@ extern int drm_debugfs_create_files(const struct drm_info_list *files,
 extern int drm_debugfs_remove_files(const struct drm_info_list *files,
 				    int count, struct drm_minor *minor);
 extern int drm_debugfs_cleanup(struct drm_minor *minor);
+#else
+static inline int drm_debugfs_init(struct drm_minor *minor, int minor_id,
+				   struct dentry *root)
+{
+	return 0;
+}
+
+static inline int drm_debugfs_create_files(const struct drm_info_list *files,
+					   int count, struct dentry *root,
+					   struct drm_minor *minor)
+{
+	return 0;
+}
+
+static inline int drm_debugfs_remove_files(const struct drm_info_list *files,
+					   int count, struct drm_minor *minor)
+{
+	return 0;
+}
+
+static inline int drm_debugfs_cleanup(struct drm_minor *minor)
+{
+	return 0;
+}
 #endif
 
 				/* Info file support */