drm/atmel-hlcdc: Compile suspend/resume for PM_SLEEP only

If PM is enabled but PM_SLEEP is disabled, the suspend/resume functions
are still unused and produce a compiler warning.
Signed-off-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Cc: <stable@vger.kernel.org> # 4.1+

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c

@@ -559,7 +559,7 @@ static int atmel_hlcdc_dc_drm_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 static int atmel_hlcdc_dc_drm_suspend(struct device *dev)
 {
 	struct drm_device *drm_dev = dev_get_drvdata(dev);