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/riotboard_defconfig b/configs/riotboard_defconfig
index 608f571..a29c238 100644
--- a/configs/riotboard_defconfig
+++ b/configs/riotboard_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/boundary/nitrogen6x/nitrogen6s1g.cfg,MX6S,DDR_MB=1024,ENV_IS_IN_MMC"
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
+CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set