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/rpi_defconfig b/configs/rpi_defconfig
index ba64c7c..b2c55cc 100644
--- a/configs/rpi_defconfig
+++ b/configs/rpi_defconfig
@@ -22,6 +22,7 @@
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
+CONFIG_CONSOLE_SCROLL_LINES=10
 CONFIG_LCD=y
 CONFIG_PHYS_TO_BUS=y
 CONFIG_OF_LIBFDT=y