turnip: Put VK_KHR_external_fence_fd stubs back

tu_ImportFenceFdKHR is used by tu_AcquireImageANDROID, which may or
may not work, but let's at least keep things compiling until somebody
has time to tie up the loose ends on the Android side.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5670>

src/freedreno/vulkan/tu_device.c

@@ -2483,6 +2483,25 @@ tu_GetMemoryFdPropertiesKHR(VkDevice _device,
    return VK_SUCCESS;
 }
 
+VkResult
+tu_ImportFenceFdKHR(VkDevice _device,
+                    const VkImportFenceFdInfoKHR *pImportFenceFdInfo)
+{
+   tu_stub();
+
+   return VK_SUCCESS;
+}
+
+VkResult
+tu_GetFenceFdKHR(VkDevice _device,
+                 const VkFenceGetFdInfoKHR *pGetFdInfo,
+                 int *pFd)
+{
+   tu_stub();
+
+   return VK_SUCCESS;
+}
+
 VkResult
 tu_ImportSemaphoreFdKHR(VkDevice _device,
                         const VkImportSemaphoreFdInfoKHR *pImportSemaphoreFdInfo)