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/dfi-bt700-q7x-151_defconfig b/configs/dfi-bt700-q7x-151_defconfig
index 6dd1c39..bddfca2 100644
--- a/configs/dfi-bt700-q7x-151_defconfig
+++ b/configs/dfi-bt700-q7x-151_defconfig
@@ -63,4 +63,5 @@
 CONFIG_FRAMEBUFFER_SET_VESA_MODE=y
 CONFIG_FRAMEBUFFER_VESA_MODE_114=y
 CONFIG_CFB_CONSOLE=y
+CONFIG_CONSOLE_SCROLL_LINES=5
 CONFIG_USE_PRIVATE_LIBGCC=y