ggml-cuda : disable MMQ on devices with less than 48 KiB shared memory (#26141)

ggml_cuda_should_use_mmq() selects MMQ purely from the quantization
type. The current MMQ configurations are designed and maintained against
a minimum of 48 KiB per-block shared memory, the limit provided by
NVIDIA Pascal GPUs and later. On devices that report less, no supported
MMQ tile fits and mul_mat_q_switch_J() aborts when every tile size
exceeds the device's per-block shared memory budget.

Disable MMQ when smpbo < 48 KiB so the caller falls back to the BLAS
path instead of hitting GGML_ABORT. Some current MUSA QY1 devices
report only 28 KiB and are covered by this guard.

Reproduced on a Moore Threads MTT S70 (arch mp_21, 28 KiB shared memory
per block) with an RWKV-7 0.1B Q8_0 model:

  $ llama-bench -m rwkv7-g1d-0.1b-Q8_0.gguf -p 128 -n 0
  J_best=0
  ggml/src/ggml-cuda/template-instances/../mmq.cuh:1521: fatal error
  (core dumped)

Only prefill (batch > 1) is affected; token generation is fine. After
the fix the same device falls back to the BLAS path:

  Q8_0    pp128 1470.7 t/s, tg8 55.3 t/s   (was: abort)
  FP16    unchanged
  Q4_K_M  unchanged

This matches a -DGGML_CUDA_FORCE_CUBLAS=ON build (pp128 1464.2 t/s),
which confirms the fallback path is the one being taken.

This is not MUSA-specific: any device with less than 48 KiB per-block
shared memory is affected.

Co-authored-by: KakaruHayate <KakaruHayate@users.noreply.github.com>

ggml/src/ggml-cuda/mmq.cu

@@ -296,6 +296,15 @@ bool ggml_cuda_should_use_mmq(enum ggml_type type, int cc, int64_t ne11, int64_t
         return false;
     }
 
+    // MMQ tiles require at least 48 KiB per-block shared memory; fall back to BLAS otherwise.
+    {
+        const int    id    = ggml_cuda_get_device();
+        const size_t smpbo = ggml_cuda_info().devices[id].smpbo;
+        if (smpbo < 48 * 1024) {
+            return false;
+        }
+    }
+
     if (turing_mma_available(cc)) {
         return true;
     }