Not sure if you meant to point out something else but initramfs or ramdisks are loaded on to RAM itself which is already up and running at that point. RAM initialization is usually initiated by early boot firmware and information about the physical address map is eventually passed on to the OS kernel which later sets up paging (virtual memory).

That’s exactly what is done during bring up of new SoCs. Memory controllers are either non-functional in early prototypes or a miniature design is put into a bunch of FPGAs with only a single core and caches. The cache lines and TLB entries are primed and pinned with all relevant code and data pages before booting up a kernel.