drm/kms: add crtc disable function

More explicit than dpms. Same as the encoder disable function.

Need this to explicity disconnect plls from crtcs for reuse when you
plls:crtcs ratio isn't 1:1.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drm_crtc_helper.h b/include/drm/drm_crtc_helper.h
index 1121f77..7e3c976 100644
--- a/include/drm/drm_crtc_helper.h
+++ b/include/drm/drm_crtc_helper.h
@@ -63,6 +63,9 @@
 
 	/* reload the current crtc LUT */
 	void (*load_lut)(struct drm_crtc *crtc);
+
+	/* disable crtc when not in use - more explicit than dpms off */
+	void (*disable)(struct drm_crtc *crtc);
 };
 
 struct drm_encoder_helper_funcs {