video: Add a dark-grey console colour

This is useful for highlighting something with a black background, as
is needed with cedit when using a white-on-black console. Add this as
a new colour.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/video-uclass.c b/drivers/video/video-uclass.c
index 9823673..a5b3e89 100644
--- a/drivers/video/video-uclass.c
+++ b/drivers/video/video-uclass.c
@@ -294,6 +294,9 @@
 	{ 0xff, 0x00, 0xff },  /* bright magenta */
 	{ 0x00, 0xff, 0xff },  /* bright cyan */
 	{ 0xff, 0xff, 0xff },  /* white */
+
+	/* an extra one for menus */
+	{ 0x40, 0x40, 0x40 },  /* dark gray */
 };
 
 u32 video_index_to_colour(struct video_priv *priv, enum colour_idx idx)