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/aristainetos2c_defconfig b/configs/aristainetos2c_defconfig
index eba3ea8..7cb1df5 100644
--- a/configs/aristainetos2c_defconfig
+++ b/configs/aristainetos2c_defconfig
@@ -63,6 +63,7 @@
 CONFIG_ENV_WRITEABLE_LIST=y
 CONFIG_ENV_ACCESS_IGNORE_FORCE=y
 CONFIG_VERSION_VARIABLE=y
+CONFIG_ARP_TIMEOUT=200
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_APBH_DMA=y
 CONFIG_APBH_DMA_BURST=y