drm/radeon: Use drm_fb_helper_lastclose() and _poll_changed()

This driver can use drm_fb_helper_lastclose() in its .lastclose function.
It can also use drm_fb_helper_output_poll_changed() as its
.output_poll_changed callback.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index ddfe91ef..dfda5e0 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -32,6 +32,7 @@
 
 #include <linux/pm_runtime.h>
 #include <drm/drm_crtc_helper.h>
+#include <drm/drm_fb_helper.h>
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_edid.h>
 
@@ -1362,15 +1363,9 @@ radeon_user_framebuffer_create(struct drm_device *dev,
 	return &radeon_fb->base;
 }
 
-static void radeon_output_poll_changed(struct drm_device *dev)
-{
-	struct radeon_device *rdev = dev->dev_private;
-	radeon_fb_output_poll_changed(rdev);
-}
-
 static const struct drm_mode_config_funcs radeon_mode_funcs = {
 	.fb_create = radeon_user_framebuffer_create,
-	.output_poll_changed = radeon_output_poll_changed
+	.output_poll_changed = drm_fb_helper_output_poll_changed,
 };
 
 static const struct drm_prop_enum_list radeon_tmds_pll_enum_list[] =