CONFIG_CON_ZERO_CHAN is not available for thedefaultarchitecture x86.
Result is shown for architecture um

Default main console channel initialization

configname: CONFIG_CON_ZERO_CHAN

Linux Kernel Configuration
└─>UML Character Devices
└─>Default main console channel initialization
In linux kernel since version 2.6.12  
This is the string describing the channel to which the main console
will be attached by default. This value can be overridden from the
command line. The default value is "fd:0,fd:1", which attaches the
main console to stdin and stdout.
It is safe to leave this unchanged.