[U-Boot] Enabling of KGDB using U-Boot

I want to know U-boot user mode configuration to enable KGDB. Is there any solution to my problem. actually I have seen some thing like this CFG_CMD_KGDB* kgdb

in u-boot readme. this CFG_CMD_KGDB is 'or'ed to CONFIG_COMMANDS but I dont know the proper procedure.