[310p]: add rmsnorm gated fallback and unit test (#7424)

### What this PR does / why we need it?
RFC #7394
310P cannot use the fused `rmsnormgated` operator and must fall back to
the native implementation.

### Does this PR introduce _any_ user-facing change?
NO
### How was this patch tested?
ut
- vLLM version: v0.17.0
- vLLM main:
4497431df6

---------

Signed-off-by: Tflowers-0129 <2906339855@qq.com>

tests/ut/_310p/ops/test_layernorm_310.py

@@ -0,0 +1,41 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+import torch
+from vllm.config import set_current_vllm_config
+from vllm.model_executor.layers.layernorm import RMSNormGated
+
+from vllm_ascend._310p.ops.layernorm import AscendRMSNormGated310
+
+
+@pytest.fixture(autouse=True)
+def default_vllm_config():
+    mock_config = MagicMock()
+    mock_config.compilation_config.custom_ops = ["all"]
+    with set_current_vllm_config(mock_config):
+        yield mock_config
+
+
+def test_rmsnorm_gated_310_forward_oot_uses_forward_native():
+    layer = AscendRMSNormGated310(hidden_size=8, eps=1e-5)
+    x = torch.randn(2, 8, dtype=torch.float32)
+    z = torch.randn(2, 8, dtype=torch.float32)
+    expected = torch.randn(2, 8, dtype=torch.float32)
+
+    with patch.object(RMSNormGated, "forward_native", autospec=True, return_value=expected) as mock_forward_native:
+        out = layer.forward_oot(x, z)
+
+    mock_forward_native.assert_called_once_with(layer, x, z)
+    assert out is expected
+
+
+def test_rmsnorm_gated_310_forward_oot_uses_forward_native_without_gate():
+    layer = AscendRMSNormGated310(hidden_size=8, eps=1e-5)
+    x = torch.randn(2, 8, dtype=torch.float32)
+    expected = torch.randn(2, 8, dtype=torch.float32)
+
+    with patch.object(RMSNormGated, "forward_native", autospec=True, return_value=expected) as mock_forward_native:
+        out = layer.forward_oot(x, None)
+
+    mock_forward_native.assert_called_once_with(layer, x, None)
+    assert out is expected