[MLBEDSW-4530] Improve --verbose-graph output

Improved --verbose-graph output by adding labels to each print.

Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
Change-Id: I49039ff6af1c06f49208591f02effa4ff73f982a
diff --git a/ethosu/vela/graph_optimiser.py b/ethosu/vela/graph_optimiser.py
index 99d4bf0..f4472f9 100644
--- a/ethosu/vela/graph_optimiser.py
+++ b/ethosu/vela/graph_optimiser.py
@@ -1680,7 +1680,7 @@
 
 def optimise_graph_a(nng, arch, verbose_graph=False):
     if verbose_graph:
-        nng.print_graph()
+        nng.print_graph("Before Graph Optimization")
 
     pre_process_list = [
         supported_operator_check,
@@ -1783,5 +1783,5 @@
         rewrite_graph.visit_graph_post_order(sg.output_tensors, arch, [], [check_reshapes, _record_optimised])
 
     if verbose_graph:
-        nng.print_graph()
+        nng.print_graph("After Graph Optimization")
     return nng