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/net2big_v2_defconfig b/configs/net2big_v2_defconfig
index dddc129..f038327 100644
--- a/configs/net2big_v2_defconfig
+++ b/configs/net2big_v2_defconfig
@@ -47,6 +47,7 @@
 CONFIG_ENV_SPI_MAX_HZ=20000000
 CONFIG_ENV_ADDR=0x70000
 CONFIG_NETCONSOLE=y
+CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
 CONFIG_DM=y
 CONFIG_SATA_MV=y
 CONFIG_SYS_SATA_MAX_DEVICE=2