radeon: Try harder to ensure we reclock in vblank

The vblank interrupt on r600 doesn't seem to be especially reliable, so
perform some sanity checks before the actual reclock.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
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 bed84b3..93ac88eb 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -175,6 +175,7 @@
 void radeon_pm_compute_clocks(struct radeon_device *rdev);
 void radeon_combios_get_power_modes(struct radeon_device *rdev);
 void radeon_atombios_get_power_modes(struct radeon_device *rdev);
+bool radeon_pm_in_vbl(struct radeon_device *rdev);
 bool radeon_pm_debug_check_in_vbl(struct radeon_device *rdev, bool finish);
 void radeon_sync_with_vblank(struct radeon_device *rdev);