CONFIG_HAVE_PLAT_FW_INIT_CMDLINE is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_HAVE_PLAT_FW_INIT_CMDLINE (not configurable)

configname: CONFIG_HAVE_PLAT_FW_INIT_CMDLINE

Linux Kernel Configuration
└─>HAVE_PLAT_FW_INIT_CMDLINE
In linux kernel since version 5.1 (release Date: 2019-05-05)