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/cobra5272_defconfig b/configs/cobra5272_defconfig
index ce1c4e0..98fd386 100644
--- a/configs/cobra5272_defconfig
+++ b/configs/cobra5272_defconfig
@@ -19,6 +19,7 @@
 CONFIG_CMD_PING=y
 CONFIG_ENV_ADDR=0xFFE04000
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
 CONFIG_SYS_BR0_PRELIM_BOOL=y
 CONFIG_SYS_BR0_PRELIM=0xFFE00201
 CONFIG_SYS_OR0_PRELIM=0xFFE00014