video: panel: Add a simple panel driver

Most panels are very simple - they just have a power supply and a backlight.
Add a driver which supports this and implements the enable_backlight()
method.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/Makefile b/drivers/video/Makefile
index d29280c..6658e96 100644
--- a/drivers/video/Makefile
+++ b/drivers/video/Makefile
@@ -8,7 +8,7 @@
 ifdef CONFIG_DM
 obj-$(CONFIG_DISPLAY_PORT) += dp-uclass.o
 obj-$(CONFIG_DM_VIDEO) += backlight-uclass.o
-obj-$(CONFIG_DM_VIDEO) += panel-uclass.o
+obj-$(CONFIG_DM_VIDEO) += panel-uclass.o simple_panel.o
 obj-$(CONFIG_DM_VIDEO) += video-uclass.o vidconsole-uclass.o console_normal.o
 obj-$(CONFIG_DM_VIDEO) += video_bmp.o
 ifdef CONFIG_DM_VIDEO