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/x530_defconfig b/configs/x530_defconfig
index b12f492..e932db2 100644
--- a/configs/x530_defconfig
+++ b/configs/x530_defconfig
@@ -50,6 +50,7 @@
 CONFIG_CMD_UBI=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_ADDR=0x100000
+CONFIG_ARP_TIMEOUT=200
 CONFIG_SPL_OF_TRANSLATE=y
 CONFIG_DM_I2C=y
 CONFIG_SYS_I2C_MVTWSI=y