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/crs305-1g-4s-bit_defconfig b/configs/crs305-1g-4s-bit_defconfig
index ff8f413..530ee83 100644
--- a/configs/crs305-1g-4s-bit_defconfig
+++ b/configs/crs305-1g-4s-bit_defconfig
@@ -32,6 +32,7 @@
 CONFIG_CMD_UBI=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_ARP_TIMEOUT=200
 CONFIG_BLK=y
 CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_BOOTCOUNT_ENV=y