Remove wrappers

[niwis]

Several IPs internally instantiate a more generic version, leaving unneeded ports tied or unconnected. To ensure that only the required logic is instantiated, cross-boundary optimisations and constant propagation are needed, putting a lot of weight on the tools, which often do not meet expectations.

Therefore, restructure the IPs that currently rely on wrappers in a more tool-friendly manner (i.e. using parameters). These IPs are

• spill_reg
• stream_fifo
• shift_reg
• stream_arbiter
• rstgen
• stream_join
• edge_propagator