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/bitmain_antminer_s9_defconfig b/configs/bitmain_antminer_s9_defconfig
index f3d5e5d..1c76578 100644
--- a/configs/bitmain_antminer_s9_defconfig
+++ b/configs/bitmain_antminer_s9_defconfig
@@ -59,6 +59,7 @@
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
 CONFIG_BOOTP_SERVERIP=y
 CONFIG_SPL_DM_SEQ_ALIAS=y
 CONFIG_BOOTCOUNT_LIMIT=y