CONFIG_NIOS2_PASS_CMDLINE is not available for thedefaultarchitecture x86.
Result is shown for architecture nios2

Passed kernel command line from u-boot

configname: CONFIG_NIOS2_PASS_CMDLINE

Linux Kernel Configuration
└─>Processor type and features
└─>Passed kernel command line from u-boot
In linux kernel since version 3.19 (release Date: 2015-02-08)  
Use bootargs env variable from u-boot for kernel command line.
will override "Default kernel command string".
Say N if you are unsure.