This changes the format for FIRRTL external modules to move parameter
values to the site of instantiation as opposed to being declared along
with the extmodule definition.  This has the added benefit of removing
the "defname" as this is now unified with the name of the external
module.

Signed-off-by: Schuyler Eldridge <[email protected]>

Also allow for SInt parameters.

Update EBNF grammar for external module parameters.

Make parameter types explicitly boxed.  Restrict the locations where
parameter types can show up to nodes and external module parameters.
Allow aggregate, passive parameter types.

Add a new parameter primitive operation section.  This is presently
incomplete, but includes a single `primAdd` operation to show how this
would work.

Update the EBNF grammar and the FIRRTL syntax highlighting XML file.