rockchip: video: Check for device in use

Check whether a display device is in use before using it. Add a comment as
to why two displays cannot currently be used at the same time.

This allows us to remove the device-tree change that disables vopb on
jerry.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/dts/rk3288-veyron-chromebook.dtsi b/arch/arm/dts/rk3288-veyron-chromebook.dtsi
index bbbc2f4..f88a868 100644
--- a/arch/arm/dts/rk3288-veyron-chromebook.dtsi
+++ b/arch/arm/dts/rk3288-veyron-chromebook.dtsi
@@ -13,6 +13,8 @@
 / {
 	aliases {
 		i2c20 = &i2c_tunnel;
+		video0 = &vopl;
+		video1 = &vopb;
 	};
 
 	gpio_keys: gpio-keys {