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/rock2_defconfig b/configs/rock2_defconfig
index fa2ed0d..1883f07 100644
--- a/configs/rock2_defconfig
+++ b/configs/rock2_defconfig
@@ -64,6 +64,7 @@
 CONFIG_DM_VIDEO=y
 CONFIG_DISPLAY=y
 CONFIG_VIDEO_ROCKCHIP=y
+CONFIG_CONSOLE_SCROLL_LINES=10
 CONFIG_USE_TINY_PRINTF=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_ERRNO_STR=y