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/pic32mzdask_defconfig b/configs/pic32mzdask_defconfig
index 4efddc0..6380725 100644
--- a/configs/pic32mzdask_defconfig
+++ b/configs/pic32mzdask_defconfig
@@ -31,6 +31,7 @@
 # CONFIG_ISO_PARTITION is not set
 # CONFIG_EFI_PARTITION is not set
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_ARP_TIMEOUT=500
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_CLK=y
 CONFIG_MMC=y