MLBEDSW-2528: MLCE-219: Custom operator pass through

 - Fixed custom operator pass through
 - Added error printing functions for operators and tensor
 - Minor cleanup of custom exception handling

Signed-off-by: Tim Hall <tim.hall@arm.com>
Change-Id: Idf295df1e4c544381dc480244d880c32fb285e38
diff --git a/ethosu/vela/npu_serialisation.py b/ethosu/vela/npu_serialisation.py
index 08dc0d3..18d38f3 100644
--- a/ethosu/vela/npu_serialisation.py
+++ b/ethosu/vela/npu_serialisation.py
@@ -141,7 +141,7 @@
             for op in ps.ops:
                 if op.type == "NpuOp":
                     callee = op.attrs["subgraph"]
-                    op.attrs["custom_options"] = {"type": op.type}
+                    op.attrs["custom_type"] = op.type
 
                     sz = 0
                     for tens in [callee.scratch_tensor, callee.flash_tensor, callee.command_stream_tensor]: