video: Allow driver to specify the line length

At present line_length is always calculated in video_post_probe(). But
some hardware may use a different line length, e.g. with a 1366-wide
display.

Allow the driver to set this value if needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
diff --git a/include/video.h b/include/video.h
index 3f9139e..1d57b48 100644
--- a/include/video.h
+++ b/include/video.h
@@ -61,7 +61,9 @@
  * @font_size:	Font size in pixels (0 to use a default value)
  * @fb:		Frame buffer
  * @fb_size:	Frame buffer size
- * @line_length:	Length of each frame buffer line, in bytes
+ * @line_length:	Length of each frame buffer line, in bytes. This can be
+ *		set by the driver, but if not, the uclass will set it after
+ *		probing
  * @colour_fg:	Foreground colour (pixel value)
  * @colour_bg:	Background colour (pixel value)
  * @flush_dcache:	true to enable flushing of the data cache after