Add support for parsing enum parameter types

[imphil]

It looks like the type parser isn't able to parse enum types in parameter declarations.

Failing rST code:

.. verilog:parameter:: parameter ibex_pkg::regfile_e RegFile = RegFileFF

   Register file implementation select:

   * ``ibex_pkg::RegFileFF``: Generic flip-flop-based register file

Build error message:

.../integration.rst:131: WARNING: verilog:parameter: Unexpected token Token('TEXT_EXPR', '::regfile_e RegFile = RegFileFF') at column 19:
        parameter ibex_pkg::regfile_e RegFile = RegFileFF
                          ^

        Expected one of: SYM_BRACKET_L, SYM_COMMA, OP_EQUAL, SYM_PAREN_R, SYM_SEMICOLON