drm: Adding drm helper function drm_plane_from_index().

Adding drm helper function to return plane pointer from index where
index is a returned by drm_plane_index.

v2:
-avoided nested loop by adding loop count (Daniel)

v3:
-updated patch header prefix to 'drm' (Matt)

v4:
-fixed a kerneldoc issue (kbuild-internal)

Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Chandra Konduru <chandra.konduru@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index adc9ea5..ed769e7 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1264,6 +1264,7 @@
 			  bool is_primary);
 extern void drm_plane_cleanup(struct drm_plane *plane);
 extern unsigned int drm_plane_index(struct drm_plane *plane);
+extern struct drm_plane * drm_plane_from_index(struct drm_device *dev, int idx);
 extern void drm_plane_force_disable(struct drm_plane *plane);
 extern int drm_plane_check_pixel_format(const struct drm_plane *plane,
 					u32 format);