video: Set up the copy framebuffer when enabled

This framebuffer is separately mapped. Update the video post-probe
function to set this up.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/video/video-uclass.c b/drivers/video/video-uclass.c
index 341db68..0c80fd5 100644
--- a/drivers/video/video-uclass.c
+++ b/drivers/video/video-uclass.c
@@ -293,6 +293,9 @@
 
 	priv->fb_size = priv->line_length * priv->ysize;
 
+	if (IS_ENABLED(CONFIG_VIDEO_COPY) && plat->copy_base)
+		priv->copy_fb = map_sysmem(plat->copy_base, plat->size);
+
 	/* Set up colors  */
 	video_set_default_colors(dev, false);