vela: Minor refactor

 - Changed comments to docstring on QuantizationParams
 - Simplified op type to op name conversion

Signed-off-by: Tim Hall <tim.hall@arm.com>
Change-Id: I2fdf5922cc17944c9bd37917a85fdfe50a1e651d
diff --git a/ethosu/vela/tosa_mapping.py b/ethosu/vela/tosa_mapping.py
index 6710787..f635e4a 100644
--- a/ethosu/vela/tosa_mapping.py
+++ b/ethosu/vela/tosa_mapping.py
@@ -323,14 +323,12 @@
 
 tosa_operator_inv_map = {v[0]: (k, v[1]) for k, v in tosa_operator_map.items()}
 
-
-def tosa_type_name(builtin):
-    return next(k for k, v in vars(TosaOp).items() if v == builtin)
+tosa_operator_name_map = {v: k for k, v in vars(TosaOp).items()}
 
 
 # TODO will return UNKNOWN for the once that have not yet been defined in tosa_operator_map
-def optype_to_tosa_op_type(op_type):
+def optype_to_tosa_op_type(op_type: Op):
     if op_type in tosa_operator_inv_map:
-        return tosa_type_name(tosa_operator_inv_map[op_type][0])
+        return tosa_operator_name_map[tosa_operator_inv_map[op_type][0]]
     else:
         return TosaOp.UNKNOWN