I believe that you will find this (somewhat) documented in the /Documentation section of the Linux source-tree. (Look under /usr/src.)
Kernel parameters are not specified in make ...config, et al, and a moment's reflection will reveal why this is so. The purpose of a kernel-parameter is to provide some tidbit of information to the kernel, to init, or even (through /proc/cmdline, to running programs. This information is provided at boot-time and can be changed with each reboot. It doesn't have anything to do with how the kernel has been constructed ... as the various makes do.
Anyone can see what the parameter-string is. The mkinitrd script, the kernel, the init process, the /etc/rc.sysinit script, device-drivers, and any user-level program that reads /proc/cmdline can all refer to it.