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/xilinx_zynq_virt_defconfig b/configs/xilinx_zynq_virt_defconfig
index 5e035d1..5bcd17a 100644
--- a/configs/xilinx_zynq_virt_defconfig
+++ b/configs/xilinx_zynq_virt_defconfig
@@ -71,6 +71,7 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_NETCONSOLE=y
+CONFIG_SYS_FAULT_ECHO_LINK_DOWN=y
 CONFIG_SPL_DM_SEQ_ALIAS=y
 CONFIG_DFU_TIMEOUT=y
 CONFIG_DFU_MMC=y