drivers: Add OSD uclass

Some devices offer a text-based OSD (on-screen display) that can be
programmatically controlled (i.e. text displayed on).

Add a uclass to support such devices.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index ed0b21f..4e627a3 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -683,4 +683,12 @@
 	  The video output is initialized by U-Boot, and kept by the
 	  kernel.
 
+config OSD
+	bool "Enable OSD support"
+	depends on DM
+	default n
+	help
+	   This supports drivers that provide a OSD (on-screen display), which
+	   is a (usually text-oriented) graphics buffer to show information on
+	   a display.
 endmenu