drm/bridge: cdns: Mark runtime PM operations as maybe unused

Building the driver in a configuration with !PM currently causes a
warning about these operations being unused. Mark them as such to shut
up the compiler.
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180426135853.30895-1-thierry.reding@gmail.com

drivers/gpu/drm/bridge/cdns-dsi.c

@@ -1337,7 +1337,7 @@ static const struct mipi_dsi_host_ops cdns_dsi_ops = {
 	.transfer = cdns_dsi_transfer,
 };
 
-static int cdns_dsi_resume(struct device *dev)
+static int __maybe_unused cdns_dsi_resume(struct device *dev)
 {
 	struct cdns_dsi *dsi = dev_get_drvdata(dev);
 
@@ -1350,7 +1350,7 @@ static int cdns_dsi_resume(struct device *dev)
 	return 0;
 }
 
-static int cdns_dsi_suspend(struct device *dev)
+static int __maybe_unused cdns_dsi_suspend(struct device *dev)
 {
 	struct cdns_dsi *dsi = dev_get_drvdata(dev);