Add LAST_ENABLE parameter to axis-arb-mux

[jeehoonkang]

Here's the first patch for the refactoring idea for corundum discussed here: https://groups.google.com/g/corundum-nic/c/ag28auMNfro/m/1MYs-kMJDgAJ

It adds the LAST_ENABLE parameter that indicates whether the user gives the proper last signal. If this parameter is zero, it's assumed that last is always asserted. It's more efficient to set LAST_ENABLE for single-cycle transfer because the internal registers will be optimized out.

I'd like to ask if you could review this change. Thanks!

[alexforencich]

This code actually lives in this repo: https://github.com/alexforencich/verilog-axis . You'll also need to add the parameter to the wrapper generator and the testbench.

[jeehoonkang]

it seems LAST_ENABLE is already in the main branch: https://github.com/alexforencich/verilog-ethernet/commit/edaec3bd384cbd6a2664135769a31db93805d920