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/coreboot_defconfig b/configs/coreboot_defconfig
index ad51ff1..5a0bf1f 100644
--- a/configs/coreboot_defconfig
+++ b/configs/coreboot_defconfig
@@ -24,6 +24,7 @@
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_DHCP=y
+CONFIG_BOOTP_BOOTFILESIZE=y
 # CONFIG_CMD_NFS is not set
 CONFIG_CMD_PING=y
 CONFIG_CMD_TIME=y