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/devkit8000_defconfig b/configs/devkit8000_defconfig
index 6f03714..a0e423d 100644
--- a/configs/devkit8000_defconfig
+++ b/configs/devkit8000_defconfig
@@ -26,7 +26,9 @@
 CONFIG_CMD_NAND=y
 CONFIG_CMD_NAND_LOCK_UNLOCK=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_BOOTP_BOOTFILESIZE=y
 CONFIG_BOOTP_DNS2=y
+CONFIG_BOOTP_NISDOMAIN=y
 CONFIG_BOOTP_NTPSERVER=y
 CONFIG_CMD_JFFS2=y
 CONFIG_JFFS2_DEV="nand0"