drm/crtc_helper: place drm_helper_encoder_in_use() in the header file

- The symbol was already exported.
Signed-off-by: Maarten Maathuis <madman2003@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_crtc_helper.h

@@ -98,6 +98,7 @@ extern bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
 				     int x, int y,
 				     struct drm_framebuffer *old_fb);
 extern bool drm_helper_crtc_in_use(struct drm_crtc *crtc);
+extern bool drm_helper_encoder_in_use(struct drm_encoder *encoder);
 
 extern void drm_helper_connector_dpms(struct drm_connector *connector, int mode);