musa: upgrade musa sdk to rc4.2.0

[yeahdongcn]

Make sure to read the contributing guidelines before submitting a PR

This PR upgrades the MUSA SDK from rc4.0.1 to rc4.2.0.

Key updates

1. MUSA docker tags bump to rc4.2.0 and switch back to non-muDNN variant
2. New CMake options (default OFF): GGML_MUSA_GRAPHS for enabling MUSA graphs and GGML_MUSA_MUDNN_COPY for enabling muDNN copy acceleration
3. cuBLAS API alignment

Why disable muDNN by default

Although enabling muDNN can accelerate contiguous device memory copies, MUSA SDK rc4.2.0 no longer includes the fat binary and instead provides per-architecture binaries. Additionally, the performance of musaMemcpyAsync has been improved in this release, making the performance gap minimal.

Testing Done

test-backend-ops passed.

root@659744416c9a:/ws# ./build/bin/test-backend-ops 
ggml_cuda_init: GGML_CUDA_FORCE_MMQ:    no
ggml_cuda_init: GGML_CUDA_FORCE_CUBLAS: no
ggml_cuda_init: found 1 MUSA devices:
  Device 0: MTT S80, compute capability 2.1, VMM: yes
Testing 2 devices

Backend 1/2: MUSA0
  Device description: MTT S80
  Device memory: 16297 MB (15731 MB free)
  ...
  7343/7343 tests passed
  Backend MUSA0: OK
Backend 2/2: CPU
  Skipping CPU backend
2/2 backends passed
OK

All Docker builds passed.

docker build -t local/llama.cpp:full-musa --target full -f .devops/musa.Dockerfile .
docker build -t local/llama.cpp:light-musa --target light -f .devops/musa.Dockerfile .
docker build -t local/llama.cpp:server-musa --target server -f .devops/musa.Dockerfile .

Verified the server image works as expected.

docker run -p 8080:8080 -it -v ~/models:/models local/llama.cpp:server-musa -m /models/DeepSeek-R1-Distill-Qwen-7B-Q4_K_M.gguf -ngl 999

Local build with -DGGML_MUSA_GRAPHS=ON succeeded.

root@7bd6a1e5dcc0:/ws# cmake -B build -DGGML_MUSA=ON -DMUSA_ARCHITECTURES=21 -DGGML_MUSA_GRAPHS=ON
root@7bd6a1e5dcc0:/ws# cmake --build build -j $(nproc) --config Release

Local build with -DGGML_MUSA_MUDNN_COPY=ON also succeeded when using the muDNN Docker image (as expected, it would fail with the non-muDNN variant).

root@7bd6a1e5dcc0:/ws# cmake -B build -DGGML_MUSA=ON -DMUSA_ARCHITECTURES=21 -DGGML_MUSA_MUDNN_COPY=ON
root@7bd6a1e5dcc0:/ws# cmake --build build -j $(nproc) --config Release

[ggerganov]

ci change is OK