Enable Row Split Support

For multi-gpu setups, enabling row-split can have very significant performance improvements. On my machine with 3xP40, I was able to get a speedup from ~3t/s to ~10t/s. Unfortunately, it doesn't look like there's any way to get this flag (`-sm row`) down to llama.cpp, which should otherwise support this. Wondering if it's possible to either add a way to pass along flags to llama.cpp, or to have an option which enables this flag. Given the massive performance improvement that it brings though, it seems like this should be possible, and not very much work to implement. I saw that passing along flags was discussed [here](https://github.com/ollama/ollama/pull/4120#issuecomment-2094747527), but was unfortunately not implemented.