drm/rockchip: mark symbols static where possible

We get 2 warnings when building kernel with W=1:
drivers/gpu/drm/rockchip/rockchip_drm_drv.c:309:6: warning: no previous prototype for 'rockchip_drm_fb_suspend' [-Wmissing-prototypes]
drivers/gpu/drm/rockchip/rockchip_drm_drv.c:318:6: warning: no previous prototype for 'rockchip_drm_fb_resume' [-Wmissing-prototypes]

In fact, these functions are only used in the file in which they are
declared and don't need a declaration, but can be made static.
So this patch marks these functions with 'static'.
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1474789388-3284-1-git-send-email-baoyou.xie@linaro.org

drivers/gpu/drm/rockchip/rockchip_drm_drv.c

@@ -309,7 +309,7 @@ static struct drm_driver rockchip_drm_driver = {
 };
 
 #ifdef CONFIG_PM_SLEEP
-void rockchip_drm_fb_suspend(struct drm_device *drm)
+static void rockchip_drm_fb_suspend(struct drm_device *drm)
 {
 	struct rockchip_drm_private *priv = drm->dev_private;
 
@@ -318,7 +318,7 @@ void rockchip_drm_fb_suspend(struct drm_device *drm)
 	console_unlock();
 }
 
-void rockchip_drm_fb_resume(struct drm_device *drm)
+static void rockchip_drm_fb_resume(struct drm_device *drm)
 {
 	struct rockchip_drm_private *priv = drm->dev_private;