Added recursive results to perf.py

This adds -P/--propagate and -Z/--depth to perf.py for showing recursive
results, making it easy to narrow down on where spikes in performance
come from.

This ended up being a bit different from stack.py's recursive results,
as we end up with different (diminishing) numbers as we descend.

Makefile

@@ -231,7 +231,7 @@ coverage: $(GCDA)
 perf: $(BENCH_PERF)
 	$(strip ./scripts/perf.py \
 		$^ $(patsubst %,-F%,$(SRC)) \
-		-scycles \
+		-Scycles \
 		$(PERFFLAGS))
 
 .PHONY: summary sizes