[A5][bugfix] Fix fused MoE A5 MXFP8 scale normalization, load-balance routing and gating_topk ops (#7573)

### What this PR does / why we need it?
This PR fixes A5 MXFP8 MoE scale handling in the fused MoE path.

- It normalizes MXFP8 activation scales to the packed 3D layout expected
by A5 kernels, including both precomputed dynamic_scale inputs and gmm1
output scales before they are consumed by downstream grouped matmul ops.
- It also refines the MXFP8 force load-balancing path in profiling runs.
- This PR also enables npu_gating_top_k from torch_npu instead of custom
op when running ascend950 chip.
### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
CI and E2E serving tests on Ascend950DT passed.

---------

Signed-off-by: linfeng-yuan <1102311262@qq.com>

vllm_ascend/device/device_op.py

@@ -58,6 +58,40 @@ class BaseDeviceAdaptor:
             quant_mode=quant_mode,
         )
 
+    @staticmethod
+    def maybe_normalize_mxfp_scale_layout(scale: torch.Tensor | None) -> torch.Tensor | None:
+        return scale
+
+    @staticmethod
+    def moe_gating_top_k(
+        x: torch.Tensor,
+        *,
+        k: int,
+        k_group: int,
+        group_count: int,
+        group_select_mode: int,
+        renorm: int,
+        norm_type: int,
+        out_flag: bool,
+        routed_scaling_factor: float = 1.0,
+        eps: float = 1e-20,
+        bias_opt: torch.Tensor | None = None,
+    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
+        topk_weights, topk_ids, out = torch.ops._C_ascend.moe_gating_top_k(
+            x,
+            k=k,
+            k_group=k_group,
+            group_count=group_count,
+            group_select_mode=group_select_mode,
+            renorm=renorm,
+            norm_type=norm_type,
+            out_flag=out_flag,
+            routed_scaling_factor=routed_scaling_factor,
+            eps=eps,
+            bias_opt=bias_opt,
+        )
+        return topk_weights, topk_ids.to(torch.int32), out
+
     @staticmethod
     def npu_dynamic_quant(
         hidden_states: torch.Tensor,
@@ -198,6 +232,46 @@ class A5DeviceAdaptor(BaseDeviceAdaptor):
             quant_mode=quant_mode,
         )
 
+    @staticmethod
+    def maybe_normalize_mxfp_scale_layout(scale: torch.Tensor | None) -> torch.Tensor | None:
+        if scale is None or scale.ndim != 2:
+            return scale
+        if scale.shape[-1] % 2 != 0:
+            raise ValueError(f"Invalid MXFP8 scale shape: {tuple(scale.shape)}")
+        return scale.reshape(scale.shape[0], scale.shape[1] // 2, 2)
+
+    @staticmethod
+    def moe_gating_top_k(
+        x: torch.Tensor,
+        *,
+        k: int,
+        k_group: int,
+        group_count: int,
+        group_select_mode: int,
+        renorm: int,
+        norm_type: int,
+        out_flag: bool,
+        routed_scaling_factor: float = 1.0,
+        eps: float = 1e-20,
+        bias_opt: torch.Tensor | None = None,
+    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
+        topk_weights, topk_ids, out = torch_npu.npu_moe_gating_top_k(
+            x,
+            k=k,
+            bias=bias_opt,
+            k_group=k_group,
+            group_count=group_count,
+            group_select_mode=group_select_mode,
+            renorm=0,
+            norm_type=norm_type,
+            routed_scaling_factor=routed_scaling_factor,
+            eps=eps,
+        )
+        if norm_type == 0 and renorm == 1:
+            topk_weights = topk_weights / topk_weights.sum(dim=-1, keepdim=True)
+
+        return topk_weights, topk_ids.to(torch.int32), out
+
     @staticmethod
     def npu_dynamic_quant(
         hidden_states: torch.Tensor,
@@ -215,12 +289,9 @@ class A5DeviceAdaptor(BaseDeviceAdaptor):
             )
 
         if dynamic_scale is None:
-            return torch_npu.npu_dynamic_mx_quant(hidden_states, dst_type=act_quant_type)
+            hidden_states, dynamic_scale = torch_npu.npu_dynamic_mx_quant(hidden_states, dst_type=act_quant_type)
 
-        if dynamic_scale.ndim == 2:
-            dynamic_scale = dynamic_scale.reshape(dynamic_scale.shape[0], dynamic_scale.shape[1] // 2, 2)
-
-        return hidden_states, dynamic_scale
+        return hidden_states, A5DeviceAdaptor.maybe_normalize_mxfp_scale_layout(dynamic_scale)
 
     @staticmethod
     def npu_grouped_matmul_swiglu_quant(
@@ -257,7 +328,7 @@ class A5DeviceAdaptor(BaseDeviceAdaptor):
             weight_scale_dtype=FLOAT8_E8M0FNU_DTYPE,
             x_scale_dtype=FLOAT8_E8M0FNU_DTYPE,
         )
-        return out, out_scale, None
+        return out, A5DeviceAdaptor.maybe_normalize_mxfp_scale_layout(out_scale), None
 
     @staticmethod
     def get_quant_gmm2_kwargs(