video_osd: Add osd sandbox driver and tests

Add sandbox driver and tests for the new OSD uclass.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 1e2cbe7..c680666 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -692,6 +692,12 @@
 	   is a (usually text-oriented) graphics buffer to show information on
 	   a display.
 
+config SANDBOX_OSD
+	bool "Enable sandbox OSD"
+	depends on OSD
+	help
+	  Enable support for sandbox OSD device used for testing purposes.
+
 config IHS_VIDEO_OUT
 	bool "Enable IHS video out driver"
 	depends on OSD