CUDA + ggml: add sparse-fa for DSV4/GLM (llama/27970)

ggml/include/ggml.h

@@ -2453,6 +2453,12 @@ extern "C" {
     GGML_API enum ggml_prec ggml_flash_attn_ext_get_prec(
             const struct ggml_tensor * a);
 
+    // Use finite mask entries as a sparse K/V set. Set 0 to disable.
+    // n_kv_max must bound the number of finite entries in every mask row.
+    GGML_API void ggml_flash_attn_ext_set_n_kv_max(
+            struct ggml_tensor * a,
+            int32_t              n_kv_max);
+
     GGML_API void ggml_flash_attn_ext_add_sinks(
             struct ggml_tensor * a,
             struct ggml_tensor * sinks);