Convert CONFIG_ARP_TIMEOUT to Kconfig

This converts the following to Kconfig:
   CONFIG_ARP_TIMEOUT

Cc: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/clearfog_defconfig b/configs/clearfog_defconfig
index 335adc9..12d9c87 100644
--- a/configs/clearfog_defconfig
+++ b/configs/clearfog_defconfig
@@ -42,6 +42,7 @@
 CONFIG_CMD_MVEBU_BUBT=y
 # CONFIG_SPL_PARTITION_UUIDS is not set
 CONFIG_ENV_OVERWRITE=y
+CONFIG_ARP_TIMEOUT=200
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_SPL_OF_TRANSLATE=y
 CONFIG_AHCI_MVEBU=y