Convert CONFIG_SYS_FAULT_ECHO_LINK_DOWN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FAULT_ECHO_LINK_DOWN

Cc: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/km_kirkwood_128m16_defconfig b/configs/km_kirkwood_128m16_defconfig
index ef81952..470c6e6 100644
--- a/configs/km_kirkwood_128m16_defconfig
+++ b/configs/km_kirkwood_128m16_defconfig
@@ -49,6 +49,7 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_VERSION_VARIABLE=y
 CONFIG_NETCONSOLE=y
+CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
 CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_BOOTCOUNT_RAM=y
 CONFIG_KIRKWOOD_GPIO=y