Back in the days a CPU was a chest-height cabinet with another chest-height cabinet besides it, containing a magnetic drum or core memory or something, acting as RAM. That stuff moved into the CPU case, then it moved into the CPU package there's really no difference the central processing unit is still the central processing unit no matter how much stuff you include.

This was the first SoC: An ARM3 core, memory controller, IO controller, video accelerator. It's hard to find an x86 nowadays that doesn't have all of that on the package: A system processor to manage everything, multiple application cores, usually at least two memory controllers, decent to absurd amount of PCIe lanes, and a GPU. Chipsets nowadays do little more than manage power, feed the SoC its initial code, and split up some PCIe lanes to provide custom IO because keyboards don't tend to speak PCIe.