video: Begin support for measuring multiple lines of text

Update the vidconsole API so that measure() can measure multiple lines
of text. This will make it easier to implement multi-line fields in
expo.

Tidy up the function comments while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/video.c b/test/dm/video.c
index 6ce1a75..cfc831b 100644
--- a/test/dm/video.c
+++ b/test/dm/video.c
@@ -788,6 +788,7 @@
 	struct vidconsole_bbox bbox;
 	struct video_priv *priv;
 	struct udevice *dev, *con;
+	struct alist lines;
 
 	ut_assertok(uclass_get_device(UCLASS_VIDEO, 0, &dev));
 	priv = dev_get_uclass_priv(dev);
@@ -797,11 +798,13 @@
 	/* this is using the Nimbus font with size of 18 pixels */
 	ut_assertok(uclass_get_device(UCLASS_VIDEO_CONSOLE, 0, &con));
 	vidconsole_position_cursor(con, 0, 0);
-	ut_assertok(vidconsole_measure(con, NULL, 0, test_string, &bbox));
+	ut_assertok(vidconsole_measure(con, NULL, 0, test_string, &bbox,
+				       &lines));
 	ut_asserteq(0, bbox.x0);
 	ut_asserteq(0, bbox.y0);
 	ut_asserteq(0x47a, bbox.x1);
 	ut_asserteq(0x12, bbox.y1);
+	ut_asserteq(0, lines.count);
 
 	return 0;
 }