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/mx6sabresd_spl_defconfig b/configs/mx6sabresd_spl_defconfig
index 3f836ff..be73098 100644
--- a/configs/mx6sabresd_spl_defconfig
+++ b/configs/mx6sabresd_spl_defconfig
@@ -15,6 +15,7 @@
 CONFIG_BOOTDELAY=3
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
+CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y