MLBEDSW-1998: Add support for new_axis_mask

-Added support for new_axis_mask
-Added support for more than 1 bit set in new/shrink_axis mask
-Added checks for strided slice in supported operator check
-Added assert if nothing has been put on NPU

Change-Id: I66e2d04784f14d7ad82371f5d649a455d576a818
Signed-off-by: Patrik Gustavsson <patrik.gustavsson@arm.com>
diff --git a/ethosu/vela/compiler_driver.py b/ethosu/vela/compiler_driver.py
index 7f8c4ca..db669ac 100644
--- a/ethosu/vela/compiler_driver.py
+++ b/ethosu/vela/compiler_driver.py
@@ -141,6 +141,8 @@
                 sg, permanent_storage, ignore_subgraph_input_output_tensors=True, lr_graph=lr_graph_flash
             )
 
+    assert len(nng.subgraphs) > 1, "Error: No operators can be hardware accelerated; cancelling compilation"
+
     # Allocate all Npu constant tensors to the first Npu subgraph since it is
     # processed first during serialization into tensors
     first_npu_sg = nng.subgraphs[1]