Convert CONFIG_BOOTP_MAY_FAIL et al to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTP_MAY_FAIL
   CONFIG_BOOTP_VENDOREX
   CONFIG_BOOTP_BOOTFILESIZE
   CONFIG_BOOTP_NISDOMAIN
   CONFIG_BOOTP_TIMEOFFSET

Cc: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/evb-ast2500_defconfig b/configs/evb-ast2500_defconfig
index ea00185..03c5cc6 100644
--- a/configs/evb-ast2500_defconfig
+++ b/configs/evb-ast2500_defconfig
@@ -21,6 +21,7 @@
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_DHCP=y
+CONFIG_BOOTP_BOOTFILESIZE=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
 CONFIG_ENV_OVERWRITE=y