[Platform] Route pin memory availability through current_platform (#28113)

Co-authored-by: N3u0ns <N3u0ns@users.noreply.github.com>
Co-authored-by: Alex Nails <alex.nails@radixark.ai>

docs_new/docs/hardware-platforms/plugin.mdx

@@ -371,6 +371,12 @@ python -c "from sglang.srt.platforms import current_platform; print(current_plat
       <td><strong>Active</strong></td>
       <td>Get current peak memory usage in bytes</td>
     </tr>
+    <tr>
+      <td><code>is_pin_memory_available(device=None)</code></td>
+      <td><code>False</code></td>
+      <td><strong>Active</strong></td>
+      <td>Whether pinned host memory is available for a target device</td>
+    </tr>
     <tr>
       <td><code>get_torch_distributed_backend_str()</code></td>
       <td><code>raise NotImplementedError</code></td>
@@ -470,11 +476,6 @@ python -c "from sglang.srt.platforms import current_platform; print(current_plat
       <td><code>False</code></td>
       <td>Whether FP8 quantization is supported</td>
     </tr>
-    <tr>
-      <td><code>is_pin_memory_available()</code></td>
-      <td><code>True</code></td>
-      <td>Whether pinned memory is available</td>
-    </tr>
   </tbody>
 </table>