lcd: Add CONFIG_CONSOLE_SCROLL_LINES option to speed console

When the cursor position gets to the end of the LCD console we normally
scroll by one line. This adds an option to increase that value.

Console scrolling is often slow, and if a large amount of output is
being sent, increasing this option to 10 or so will speed things up
considerably.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/README b/README
index 5c03be7..037513a 100644
--- a/README
+++ b/README
@@ -1478,6 +1478,12 @@
 		here, since it is cheaper to change data cache settings on
 		a per-section basis.
 
+		CONFIG_CONSOLE_SCROLL_LINES
+
+		When the console need to be scrolled, this is the number of
+		lines to scroll by. It defaults to 1. Increasing this makes
+		the console jump but can help speed up operation when scrolling
+		is slow.
 
 - Splash Screen Support: CONFIG_SPLASH_SCREEN