Branch: poky/master
Git rev: 176a46b088135f2891983bb8540bc45389341d90

Steps:
1. create a new bsp with all the default options:  
    yocto-bsp create myqemux86 qemu
2. modify conf/bblayers.conf, BBLAYERS field, added "meta-myqemux86" directory
3. input "yocto-kernel config add myqemux86 CONFIG_MISC_DEVICES=y" 3 times
4. input "yocto-kernel config list myqemux86" to check, you will get below list:

The current set of machine-specific kernel config items for myqemux86 is:
	1) CONFIG_MISC_DEVICES=y
	2) CONFIG_MISC_DEVICES=y
	3) CONFIG_MISC_DEVICES=y

The same component "CONFIG_MISC_DEVICES" lists 3 times.

I think when add the configration, the script should first check, if this option already exists: 
If yes, only tell the customer the configration is duplicate, but not truely add it.
If no, then add it.