Re: [sv-ac] formal_list_item

The data_type is optional, because the empty string can be derived from
data_type_or_implicit.

-- Brad

>tf_port_item ::= 
>{ attribute_instance } 
>[ tf_port_direction ] data_type_or_implicit 
>port_identifier variable_dimension [ = expression ] 
>
>tf_port_direction ::= port_direction | const ref 
>
>Also, from the above bnf it looks like, date_type is not optional.