ggml-hexagon: mm for mtmd

[joeldushouyu]

Summary

This pr allows running vision models(tested with gemma4b) on Hexagon NPU.

For now, it only supports using the CDSP for doing fp16xfp32.
Note: I am fully aware that the current FP16xFP32 implementation is not the most optimal. For example, we can easily reduce unnecessary data repetition by using the vtcm as cache, but I think that should probably go into a separate pr that focuses solely on optimization.

Test

I used the f16 vision weights and q40 language weights from unsloth.

1. build hexagon in docker

cmake --preset arm64-android-snapdragon-release -B build-snapdragon
cmake --build build-snapdragon
cmake --install build-snapdragon --prefix pkg-adb/llama.cpp

2. push the weights to phone(tested with samsung s25 ultra

adb push mmproj-F16.gguf data/local/tmp/gguf
adb push gemma-3-4b-it-Q4_0.gguf /data/local/tmp/gguf
adb push hydro_1.png /data/local/tmp/gguf   #Image for testing 

3. run the run-mtmd script

E=1 NDEV=1 D=HTP0 MTMD_DEVICE=HTP0 PROF=1 V=1 M=gemma-3-4b-it-Q4_0.gguf MMPROJ=mmproj-F16.gguf IMG=hydro_1.png ./scripts/snapdragon/adb/run-mtmd.sh -p '"What is in this image."'