Add bf16 output option for dsv3_router_gemm kernel (#7999)

sgl-kernel/python/sgl_kernel/gemm.py

@@ -262,12 +262,13 @@ def qserve_w4a8_per_group_gemm(
 def dsv3_router_gemm(
     hidden_states: torch.Tensor,
     router_weights: torch.Tensor,
+    out_dtype: torch.dtype = torch.bfloat16,
 ) -> torch.Tensor:
     output = torch.empty(
         hidden_states.shape[0],
         router_weights.shape[0],
         device=hidden_states.device,
-        dtype=torch.float32,
+        dtype=out_dtype,
     )
     torch.ops.sgl_kernel.dsv3_router_gemm(
         output,