Improve --time-unit arg (#807)

src/config.py

@@ -30,3 +30,5 @@ PROJECT_NAME = "rocprofiler-compute"
 
 HIDDEN_COLUMNS = ["Tips", "coll_level"]
 HIDDEN_SECTIONS = [400, 1900, 2000]
+
+TIME_UNITS = {"s": 10**9, "ms": 10**6, "us": 10**3, "ns": 1}