qapi script: code move for generate_enum_name()

Later both qapi-types.py and qapi-visit.py need a common function
for enum name generation.

Signed-off-by: Wenchao Xia <wenchaoqemu@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

scripts/qapi.py

@@ -467,3 +467,13 @@ def guardend(name):
 
 ''',
                  name=guardname(name))
+
+def generate_enum_name(name):
+    if name.isupper():
+        return c_fun(name, False)
+    new_name = ''
+    for c in c_fun(name, False):
+        if c.isupper():
+            new_name += '_'
+        new_name += c
+    return new_name.lstrip('_').upper()