Convert CONFIG_CONSOLE_SCROLL_LINES to Kconfig

This converts the following to Kconfig:
   CONFIG_CONSOLE_SCROLL_LINES

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/colibri_t20_defconfig b/configs/colibri_t20_defconfig
index d070a27..897cd01 100644
--- a/configs/colibri_t20_defconfig
+++ b/configs/colibri_t20_defconfig
@@ -54,3 +54,4 @@
 CONFIG_G_DNL_PRODUCT_NUM=0x701a
 CONFIG_DM_VIDEO=y
 CONFIG_VIDEO_TEGRA20=y
+CONFIG_CONSOLE_SCROLL_LINES=10