drm/radeon/kms: release AGP bridge at suspend

I think it's good to release the AGP bridge at suspend
and reacquire it at resume. Also fix :
https://bugzilla.kernel.org/show_bug.cgi?id=15969

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 66a37fb..669feb6 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -576,6 +576,7 @@
  */
 int radeon_agp_init(struct radeon_device *rdev);
 void radeon_agp_resume(struct radeon_device *rdev);
+void radeon_agp_suspend(struct radeon_device *rdev);
 void radeon_agp_fini(struct radeon_device *rdev);