Build CPU only image

### What is the issue? I'd be interested in only building a CPU docker image for ppc arch. I tried to do that for arm64 but it doesn't work perfectly either so I'm wondering if that is possible at all with only one big Dockerfile as it is now? Ideally I'd like to have something like `PLATFORM=linux/arm64 TARGETARCH=arm64 DEVICE=cpu scripts/build_docker.sh` Maybe someone can enlighten me how to do this. Thank you! ### OS Linux, Docker ### GPU _No response_ ### CPU Other ### Ollama version 0.3.11