Convert CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nitrogen6q2g_defconfig b/configs/nitrogen6q2g_defconfig
index 370d748..23cd772 100644
--- a/configs/nitrogen6q2g_defconfig
+++ b/configs/nitrogen6q2g_defconfig
@@ -4,6 +4,7 @@
 CONFIG_VIDEO=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/boundary/nitrogen6x/nitrogen6q2g.cfg,MX6Q,DDR_MB=2048"
 CONFIG_BOOTDELAY=3
+CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set