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/coreboot-x86_defconfig b/configs/coreboot-x86_defconfig
index b33c5c4..964a92b 100644
--- a/configs/coreboot-x86_defconfig
+++ b/configs/coreboot-x86_defconfig
@@ -42,5 +42,6 @@
 CONFIG_USB_STORAGE=y
 CONFIG_DM_VIDEO=y
 CONFIG_VIDEO_COREBOOT=y
+CONFIG_CONSOLE_SCROLL_LINES=5
 CONFIG_USE_PRIVATE_LIBGCC=y
 CONFIG_TPM=y