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/kmcent2_defconfig b/configs/kmcent2_defconfig
index cf0748c..32c9f49 100644
--- a/configs/kmcent2_defconfig
+++ b/configs/kmcent2_defconfig
@@ -27,6 +27,7 @@
 CONFIG_CMD_MTD=y
 CONFIG_CMD_NAND_TRIMFFS=y
 CONFIG_CMD_SPI=y
+CONFIG_BOOTP_BOOTFILESIZE=y
 CONFIG_CMD_PING=y
 CONFIG_CMD_ETHSW=y
 CONFIG_CMD_CRAMFS=y