sandbox: Move CONFIG_VIDEO_SANDBOX_SDL to Kconfig

Move this option to Kconfig. This is quite simple as only sandbox uses the
driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 499d00d..ae122da 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -300,6 +300,15 @@
 	   to drive LCD panels. This framework provides support for enabling
 	   these displays where supported by the video hardware.
 
+config VIDEO_SANDBOX_SDL
+	bool "Enable sandbox video console using SDL"
+	depends on SANDBOX
+	help
+	  When using sandbox you can enable an emulated LCD display which
+	  appears as an SDL (Simple DirectMedia Layer) window. This is a
+	  console device and can display stdout output. Within U-Boot is is
+	  a normal bitmap display and can display images as well as text.
+
 config VIDEO_TEGRA124
 	bool "Enable video support on Tegra124"
 	help