where I do not mount ramfs
I was thinking /etc/fstab...
But you really mean: what do I have to select in kernel-config to have support for it - right?
There are a few alternatives to "make config"
1. make menuconfig
2. make xconfig
and possibly others
The advantage - you have a help text available with each option and don't have to go through the whole config sequentially and without a clue what means what.
I believe you where looking for: General setup -> Initramfs source file(s).
: it's better to tell what you want to achieve as a result of having "ramfs" - you might be searching in the wrong direction - and we along with you because of how you asked the question.